Migrate extension to WiX v6 APIs and SDK projects

[flcdrg]

Co-authored-by: Copilot 223556219+Copilot@users.noreply.github.com

[flcdrg]

@copilot investigate build failure and see if you can fix the cause

[Copilot]

@copilot investigate build failure and see if you can fix the cause

I investigated the failing Build workflow and pushed a fix in 4093dea.

This addresses the WiX v6 build break by switching invalid inner-text usage to attributes in Custom/ProgressText, and fixes the embedded PowerShellLibrary.wixlib path for the SDK output layout.

[flcdrg]

@copilot There are still build failures. Keep iterating until the build passes.

Also consider whether the way the build is run in the workflow needs to change given Wix now supports SDK-style projects

[Copilot]

@copilot There are still build failures. Keep iterating until the build passes.

Also consider whether the way the build is run in the workflow needs to change given Wix now supports SDK-style proje...

Pushed additional fixes in f4a1a54 (plus 20b5f06 and 327e15d) to address the remaining build issues:

• fixed remaining WiX v6 test authoring issues (Publish syntax, ProgressDlg2 reference)
• excluded legacy ProgressDlg.wxs from SDK-style compilation
• made test wix projects build the extension project first and consume its built DLL via SDK output path
• updated workflow build/msiexec paths for SDK-style outputs

Code review/CodeQL validation is clean on these changes.