[ci] Show VS & MSBuild install locations on Windows (#4833)

Context: https://github.com/xamarin/yaml-templates/blob/cf440bcf4daf0305be17280bf27854480314db77/environment/win/vs-msbuild.v1.yml

Context: https://devdiv.visualstudio.com/DevDiv/_build/results?buildId=3795214&view=logs&j=cac0e8d3-0ef5-5d2b-b57e-e8fde7204df3&t=b0ec5c6c-f5a1-5ebf-2068-57a5c78a6a85

There have been a few issues involving Xamarin.Android builds on
Windows involving problems with the Visual Studio installation or an
incorrect (older) version of MSBuild being invoked:

	##[debug]Entering Invoke-VstsTool.
	##[debug] FileName: 'C:\Windows\Microsoft.NET\Framework\v4.0.30319\msbuild.exe'
	##[debug] Arguments: '"C:\A\vs2019xam000013-1\_work\2\s\Xamarin.Android.sln" … /t:Prepare /p:AutoProvision=true /bl:C:\A\vs2019xam000013-1\_work\2\s\bin\BuildRelease\msbuild-prepare.binlog …
	##[debug] RequireExitCodeZero: 'True'
	"C:\Windows\Microsoft.NET\Framework\v4.0.30319\msbuild.exe" …
	MSBUILD : error MSB1001: Unknown switch.
	Switch: /bl:C:\A\vs2019xam000013-1\_work\2\s\bin\BuildRelease\msbuild-prepare.binlog

	For switch syntax, type "MSBuild /help"
	##[debug]Exit code: 1

We're not entirely sure why this happens.

Add a template include to `environment/win/vs-msbuild.v1.yml@yaml`,
which adds two new steps to **Windows** > **Build and Smoke Test**:

  * `Env: Create Write-MSBuildPath.ps1`, which creates a
    PowerShell script

  * `Env: Visual Studio (Windows)`, which invokes the
    `Write-MSBuildPath.ps1` script, printing out information about
    the currently installed Visual Studio instances.

The new steps provide visibility into the Visual Studio and MSBuild
installations, utilizing `vswhere` as a means to enumerate and obtain
the Visual Studio installs on the agent.  Additionally, the template
being called leverages code from the MSBuild task to locate the version
of MSBuild that will be used:

	Visual Studio installations based on the vswhere.exe command
	…
	[
	  {
	    …
	    "installationPath": "C:\\Program Files (x86)\\Microsoft Visual Studio\\2019\\Enterprise",
	…

	Visual Studio installed products:
	  Microsoft.VisualStudio.Product.Enterprise 16.6.30114.105: C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise
	      IsComplete: True
	      IsLaunchable: True
	      IsRebootRequired: False
	    MSBuild: C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\MSBuild\Current\Bin\msbuild.exe

Author: mjbond-msft

build-tools/automation/azure-pipelines.yaml

@@ -271,6 +271,8 @@ stages:
       displayName: downgrade XA to stable
       ignoreLASTEXITCODE: true
 
+    - template: environment/win/vs-msbuild.v1.yml@yaml   # Display (in log) VS installation(s) including installation status with associated MSBuild location(s)
+
     - task: MSBuild@1
       displayName: msbuild Xamarin.Android /t:Prepare
       inputs:

build-tools/automation/yaml-templates/run-msbuild-win-tests.yaml

@@ -17,6 +17,8 @@ jobs:
 
     - template: clean.yaml
 
+    - template: environment/win/vs-msbuild.v1.yml@yaml   # Display (in log) VS installation(s) including installation status with associated MSBuild location(s)
+
     - template: setup-test-environment.yaml
       parameters:
         provisionExtraArgs: -vv PROVISIONATOR_VISUALSTUDIO_LOCATION="$(VSINSTALLDIR)" -f