Contributing using Eclipse+Windows is hard

This is an umbrella issue for the hurdles developers who want to develop in the Closure Compiler codebase using Eclipse on Windows will encounter. It's just taken me, a moderately seasoned external contributor, about half a day to get developing properly from scratch.

First, ideally the "mvn eclipse:eclipse" command would create eclipse configs that just worked, but I don't know how to solve that. Instead, the README has some fairly arduous steps needed to correct the project configuration.

Then, if you want to run tests, either via `mvn` or individually from within Eclipse, you get a bunch of failures mostly relating to filesystem absolute paths, line separators, and one relating to case insensitivity:
```
Failed tests:
DepsGeneratorTest.testWithDepsAndSources:165 expected:<.../my-project/deps1.js[
goog.addDependency('../prescanned1/file1.js', ['dep.string'], []);
goog.addDependency('../prescanned1/file2.js', [], []);

// Included from: /base/my-project/deps2.js]
goog.addDependency(...> but was:<.../my-project/deps1.js[
goog.addDependency('../prescanned1/file1.js', ['dep.string'], []);
goog.addDependency('../prescanned1/file2.js', [], []);

]/ Included from: /base/my-project/deps2.js
goog.addDependency(...>
TranspileResultTest.testEquals:38 TranspileResut{path=a, original=b, transpiled=c, sourceMapURL=d} [group 1, item 1] must not be Object#equals to TranspileResut{path=A, original=b, transpiled=c, sourceMapURL=d} [group 2, item 1]
Tests in error:
SourceFileTest.testSourceFileResolvesZipEntries:119 » NoSuchFile C:\Users\STEV...
DepsGeneratorTest.testDuplicateProvides:337->doErrorMessagesRun:320 » IllegalArgument
DepsGeneratorTest.testDuplicateProvidesErrorThrownIfBadClosurePathSpecified:358->doErrorMessagesRun:320 » IllegalArgument
DepsGeneratorTest.testDuplicateProvidesSameFile:401->doErrorMessagesRun:320 » IllegalArgument
DepsGeneratorTest.testDuplicateRequire:412->doErrorMessagesRun:320 » IllegalArgument
DepsGeneratorTest.testSameFileProvideRequire:423->doErrorMessagesRun:320 » IllegalArgument
DepsGeneratorTest.testUnknownNamespace:433->doErrorMessagesRun:320 » IllegalArgument
ArrayIndexOfToIncludesTest.test_refactorings:41 » IllegalArgument filenameToCo...
ArrayPrototypeSliceToArrayFromTest.test_refactorings:41 » IllegalArgument file...
ChaiExpectToAssertTest.test_refactorings:41 » IllegalArgument filenameToCodeMa...
NavigationalXssSinksRefactoringTest.testModuleRefactoring:51 » IllegalArgument
NavigationalXssSinksRefactoringTest.test_refactorings:41 » IllegalArgument fil...
SetLocationHrefTest.test_refactorings:42 » IllegalArgument filenameToCodeMap m...
StringIndexOfToIncludesTest.test_refactorings:41 » IllegalArgument filenameToC...

Tests run: 12818, Failures: 2, Errors: 14, Skipped: 0
```

* IllegalArguments are mostly because: PathUtil.makeAbsolute() and isAbsolute() don't work together for Windows drive letter based paths;
* DepsGeneratorTest.testWithDepsAndSources fails because println() is used in DepsGenerator, producing `\r\n` on Windows, but `DepsGeneratorTest.LINE_JOINER` has `\n` hard-coded (I suppose changing this to read `line.separator` would work here);
* TranspileResultTest fails because `Path` 'A' and 'a' are considered equal on Windows.
* StringIndexOfToIncludesTest confuses path separator `/` with `\`
* etc.

When working with a fork or developing a PR, you need to `mvn -DskipTests` and if you do run with tests, it's hard to see whether your fork has contributed to the failures.

Updated since #2753.