[MWRAPPER-45] Migrate/Sync startup scripts with Maven 4

**[Unassigned Developer](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=unassigned-developer)** opened **[MWRAPPER-45](https://issues.apache.org/jira/browse/MWRAPPER-45?redirect=false)** and commented

The scripts are Maven 3 based. Maven 4 has simplified the scripts and introduced consistency improvements. We should port those over for version 4?!

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**Affects:** 3.1.0

**Issue Links:**
- [MNG-7193](https://issues.apache.org/jira/browse/MNG-7193) Introduce MAVEN_ARGS environment variable

- [MWRAPPER-99](https://issues.apache.org/jira/browse/MWRAPPER-99) Support MAVEN_ARGS environment variable

- [MWRAPPER-61](https://issues.apache.org/jira/browse/MWRAPPER-61) let mvnw call mvn directly, without maven-wrapper.jar

**Remote Links:**
- [Sample PR #1
](https://github.com/apache/maven/pull/637#issuecomment-999358494)
- [Sample PR #2
](https://github.com/apache/maven/pull/636#issuecomment-999358807)
- [Next PR #3
](https://github.com/apache/maven/pull/1002)

Start by locating the Maven 3-based startup scripts in the wrapper and compare them with Maven 4's simplified scripts, using the linked sample PRs as context. Review MWRAPPER-45 alongside MNG-7193, MWRAPPER-99, and MWRAPPER-61; done means the wrapper scripts are synchronized with Maven 4's consistency improvements without regressing existing startup behavior.

Written by the indexing model from the issue text.