[MNG-7541] Add Maven 4 PowerShell launcher

[wilx]

Reimplements and completes the PowerShell launcher work originally contributed
by @JurrianFahner in #878, updated for the current Maven 4 launcher. Fixes #8909.

This adds PowerShell equivalents for the Maven launcher and its mode wrappers,
preserves Maven's argument/configuration behavior, packages the scripts, and
tests them with PowerShell 7 and Windows PowerShell 5.1 in CI.

Testing:

• PowerShell launcher harness passed against the assembled distribution on
  Java 17 and Java 21.
• The Maven reactor and distribution package build passed.
• Core ITs: 1,044/1,046 passed; two unrelated tests could not resolve the
  unstaged maven-testing:4.1.0-SNAPSHOT fixture.

Following this checklist to help us incorporate your contribution quickly and
easily:

• This pull request addresses one issue without pulling in other changes.

• The pull request description explains what the change does, how, and why.

• The commit has a meaningful subject line and body.

• Tests cover the behavioral changes.

• mvn verify passes without exceptions.

• The Core IT suite passes completely.

• I hereby declare this contribution to be licenced under the Apache
  License Version 2.0, January
  2004.

• In any other case, please file an Apache Individual Contributor License
  Agreement.

[gnodet]

Well-crafted PowerShell launcher that correctly mirrors the bash/cmd launcher behavior. The complete set of wrappers (mvn.ps1, mvnDebug.ps1, mvnenc.ps1, mvnsh.ps1, mvnup.ps1, mvnyjp.ps1) properly delegates with the appropriate mode flags, matching the structure of their bash counterparts.

A few minor observations (none blocking):

• ConvertFrom-MavenOptionString is a clean reimplementation of shell-style word splitting with correct quote awareness.
• MAVEN_ARGS suppression for non-MavenCling modes (line 317-319) correctly matches both bash and cmd behavior.
• CI integration is well-positioned: tests run after distribution assembly, gated to Java 17, covering both pwsh (cross-platform) and powershell (Windows 5.1).
• The test harness avoids a Pester dependency with custom assertions — pragmatic choice for CI portability. Coverage is thorough: syntax validation, exit code propagation, quoted option preservation, POM selection, project base directory discovery, debug/specialized wrapper delegation, RC file loading, and MAVEN_SKIP_RC.

This review was generated by an AI agent and may contain inaccuracies. Please verify all suggestions before applying.

Claude Code on behalf of gnodet