Potential Fix for CommunityToolkit#262 - Remove UWP target from WinUI…

… packages

Adds a 'all-uwp' target to UseTargetFrameworks.ps1
Adds better documentation to UseTargetFrameworks.ps1
Conditionally selects the set of platforms to build for in the CI based on if running the UWP or WinUI package job

Scripts/UseTargetFrameworks.ps1

@@ -1,7 +1,30 @@
+<#
+.SYNOPSIS
+    Changes the target frameworks to build for each package created within the repository.
+.DESCRIPTION
+    By default, only the UWP, Windows App SDK, and WASM heads are built to simplify dependencies 
+    needed to build projects within the repository. The CI will enable all targets to build a package
+    that works on all supported platforms.
+    
+    Note: Projects which rely on target platforms that are excluded will be unable to build.
+.PARAMETER targets
+    List of targets to set as TFM platforms to build for. This can also be 'all', 'all-uwp', or blank.
+    When run as blank, teh defaults (uwp, winappsdk, wasm) will be used.
+    'all' and 'all-uwp' shouldn't be used with other targets or each other.
+.PARAMETER allowGitChanges
+    Enabling this flag will allow changes to the props file to be checked into source control.
+    By default the file is ignored so local changes to building don't accidently get checked in.
+.EXAMPLE
+    C:\PS> .\UseTargetFrameworks winappsdk
+    Build targets for just the WindowsAppSDK.
+.NOTES
+    Author: Windows Community Toolkit Labs Team
+    Date:   April 8, 2022
+#>
 Param (
     [Parameter(HelpMessage = "The target frameworks to enable.")]
-    [ValidateSet('all', 'wasm', 'uwp', 'winappsdk', 'wpf', 'gtk', 'macos', 'ios', 'droid')]
-    [string[]]$targets = @('uwp', 'winappsdk', 'wasm'),
+    [ValidateSet('all', 'all-uwp', 'wasm', 'uwp', 'winappsdk', 'wpf', 'gtk', 'macos', 'ios', 'droid')]
+    [string[]]$targets = @('uwp', 'winappsdk', 'wasm'), # default settings
 
     [Parameter(HelpMessage = "Disables suppressing changes to the Labs.TargetFrameworks.props file in git, allowing changes to be committed.")] 
     [switch]$allowGitChanges = $false
@@ -47,6 +70,10 @@ if ($targets.Contains("all")) {
     $desiredTfmValues = $allTargetFrameworks;
 }
 
+if ($targets.Contains("all-uwp")) {
+    $desiredTfmValues = $allTargetFrameworks.Replace($UwpTfm, "");
+}
+
 if ($targets.Contains("wasm")) {
     $desiredTfmValues += $WasmTfm;
 }