[MWRAPPER-78] Rewrite mvnw.cmd in PowerShell (mvnw.ps1)

**[Jorge Solórzano](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=jorsol)** opened **[MWRAPPER-78](https://issues.apache.org/jira/browse/MWRAPPER-78?redirect=false)** and commented

More and more features in the Batch script for Windows are requiring PowerShell, one feature is the web client to download the wrapper jar, and the next one will be the sha256sum feature.

Batch scripting is showing its age and even Microsoft doesn't really want to be used anymore, PowerShell 2.0 is integrated with Windows 7 and Windows Server 2008 R2, and is released for Windows XP with Service Pack 3, Windows Server 2003 with Service Pack 2, and Windows Vista with Service Pack 1, it would make sense to migrate the Batch script into PowerShell.

There is even a PowerShell Core version that could be installed on Linux, but I'm not sure about the compatibility with older versions of Windows PowerShell, one goal could be to make it compatible with Windows 7 and higher, but honestly, I'm not sure if we should be supporting an OS that out of support.

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**Issue Links:**
- [MNG-7541](https://issues.apache.org/jira/browse/MNG-7541) Native support for PowerShell to start Maven

Start by comparing the existing mvnw.cmd entry point with the proposed mvnw.ps1 script and review how the wrapper jar is downloaded. Clarify the supported Windows PowerShell versions and preserve the current wrapper behavior, including the web-client and future sha256sum requirements; the issue provides no test path.

Written by the indexing model from the issue text.