The 'auto build' should not use Maven's target folder

The fact that the 'auto build' uses Maven's target folder is problematic. It causes independent Maven builds to fail in mysterious ways. Or even worse: the build might succeed, but the build artifacts may differ from the ones that are expected (e.g. ecj-compiled classes may end up in build artifacts, even though the Maven build itself uses javac).

Environment

• Operating System: Windows 10
• JDK version: JDK 14
• Visual Studio Code version: 1.44.0
• Java extension version: 0.59.1

Steps To Reproduce

As an example of the build that might fail:

1. git clone https://github.com/validator/htmlparser.git
2. Add Folder to Workspace... -> htmlparser
3. open a Terminal (inside VS Code) & set the JAVA_HOME environment variable to a JDK 8 installation, e.g. $Env:JAVA_HOME='C:\Program Files\Java\jdk1.8.0_202'
4. in the pom.xml, add the following under build.plugins & ignore any messages about build synchronization

      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-javadoc-plugin</artifactId>
        <version>3.2.0</version>
        <configuration>
          <doclint>none</doclint>
        </configuration>
      </plugin>

5. run mvn clean source:jar javadoc:jar package repository:bundle-create in the terminal

Note: this will not fail consistently, and quite often it will also just work. But that's simply because it's about uncontrollable interference between 2 processes.

Current Result

I've seen the build fail with 3 different kinds of errors already (note that the first one explicitly mentions that the failure is possibly caused by ecj-generated classes):

[INFO] --- maven-bundle-plugin:2.3.7:bundle (default-bundle) @ htmlparser ---
[ERROR] Bundle nu.validator.htmlparser:htmlparser:bundle:1.4 : The default package '.' is not permitted by the Import-Package syntax.
 This can be caused by compile errors in Eclipse because Eclipse creates
valid class files regardless of compile errors.
The following package(s) import from the default package [nu.validator.htmlparser.io]
[ERROR] Error(s) found in bundle configuration
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------

[INFO] --- maven-compiler-plugin:3.8.1:testCompile (default-testCompile) @ htmlparser ---
[INFO] Changes detected - recompiling the module!
[INFO] Compiling 25 source files to C:\Users\me\Desktop\htmlparser\target\test-classes
[INFO] Some messages have been simplified; recompile with -Xdiags:verbose to get full output
[INFO] -------------------------------------------------------------
[ERROR] COMPILATION ERROR :
[INFO] -------------------------------------------------------------
[ERROR] /C:/Users/me/Desktop/htmlparser/test-src/nu/validator/htmlparser/test/TokenPrinter.java:[44,8] nu.validator.htmlparser.test.TokenPrinter is not abstract and does not override abstract method endTag(ElementName) in nu.validator.htmlparser.common.TokenHandler
[ERROR] /C:/Users/me/Desktop/htmlparser/test-src/nu/validator/htmlparser/test/TokenPrinter.java:[140,28] cannot access Tokenizer
  class file for Tokenizer not found
[ERROR] /C:/Users/me/Desktop/htmlparser/test-src/nu/validator/htmlparser/test/TokenizerTester.java:[101,29] incompatible types: nu.validator.htmlparser.impl.ErrorReportingTokenizer cannot be converted 
to Tokenizer
[ERROR] /C:/Users/me/Desktop/htmlparser/test-src/nu/validator/htmlparser/test/JSONArrayTokenHandler.java:[41,8] nu.validator.htmlparser.test.JSONArrayTokenHandler is not abstract and does not override 
abstract method endTag(ElementName) in nu.validator.htmlparser.common.TokenHandler
[INFO] 4 errors
[INFO] -------------------------------------------------------------
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------

[INFO] --- maven-bundle-plugin:2.3.7:bundle (default-bundle) @ htmlparser ---
[ERROR] An internal error occurred
java.io.FileNotFoundException: C:\Users\me\Desktop\htmlparser\target\classes\nu\validator\htmlparser\annotation\package.html (The system cannot find the file specified)
    at java.io.FileInputStream.open0 (Native Method)
    at java.io.FileInputStream.open (FileInputStream.java:195)
    at java.io.FileInputStream.<init> (FileInputStream.java:138)
    at aQute.lib.osgi.FileResource.openInputStream (FileResource.java:15)
    at aQute.lib.osgi.FileResource.copy (FileResource.java:36)
    at aQute.lib.osgi.FileResource.write (FileResource.java:31)
    at aQute.lib.osgi.Jar.writeResource (Jar.java:445)
    at aQute.lib.osgi.Jar.write (Jar.java:224)
    at aQute.lib.osgi.Jar.write (Jar.java:192)
    at org.apache.felix.bundleplugin.BundlePlugin.execute (BundlePlugin.java:362)
    at org.apache.felix.bundleplugin.BundlePlugin.execute (BundlePlugin.java:264)
    at org.apache.felix.bundleplugin.BundlePlugin.execute (BundlePlugin.java:255)
    at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo (DefaultBuildPluginManager.java:137)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:210)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:156)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:148)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:117)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:81)
    at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build (SingleThreadedBuilder.java:56)
    at org.apache.maven.lifecycle.internal.LifecycleStarter.execute (LifecycleStarter.java:128)
    at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:305)
    at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:192)
    at org.apache.maven.DefaultMaven.execute (DefaultMaven.java:105)
    at org.apache.maven.cli.MavenCli.execute (MavenCli.java:957)
    at org.apache.maven.cli.MavenCli.doMain (MavenCli.java:289)
    at org.apache.maven.cli.MavenCli.main (MavenCli.java:193)
    at sun.reflect.NativeMethodAccessorImpl.invoke0 (Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke (NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke (DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke (Method.java:498)
    at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced (Launcher.java:282)
    at org.codehaus.plexus.classworlds.launcher.Launcher.launch (Launcher.java:225)
    at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode (Launcher.java:406)
    at org.codehaus.plexus.classworlds.launcher.Launcher.main (Launcher.java:347)
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------

Expected Result

The build always succeeds and none of the build artifacts contain any ecj-generated classes.

Start by reproducing the interference with the htmlparser pom.xml and the Maven command listed in the issue while observing the extension's auto-build output. Trace the auto-build entry point in the Java extension and determine how its output overlaps with Maven's target folder. Done means the Maven build consistently succeeds and its artifacts contain no ECJ-generated classes.