[MWRAPPER-106] Consistent semantics

**[Delany](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=delany)** opened **[MWRAPPER-106](https://issues.apache.org/jira/browse/MWRAPPER-106?redirect=false)** and commented

Two scripts are provided: mvnw and mvnw.cmd. Presumably the only difference between them is one is used on Linux OS and the other on Windows OS.

They should not have different requirements of the maven-wrapper.properties file, for example.

mvnw allows a property to be repeated, while mvnw.cmd will fail the build with an error if a duplicate is defined:

```
ConvertFrom-StringData : Data item 'distributionUrl' in line 'distributionUrl=https://nexus.synope.com/repository/tools/maven/apache-maven-3.9.2-SNAPSHOT-bin.zip' is already defined.
At line:54 char:91
+ ... vn/wrapper/maven-wrapper.properties" | ConvertFrom-StringData).distri ...
+                                            ~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidOperation: (:) [ConvertFrom-StringData], PSInvalidOperationException
    + FullyQualifiedErrorId : InvalidOperation,Microsoft.PowerShell.Commands.ConvertFromStringDataCommand
ECHO is on.
Cannot start maven from wrapper
```

---

**Affects:** 3.2.0