[ci] Fail build if any git tracked files were modified. (#9661)

When running `xaprepare` on Windows, your local `git` tree ends up
dirty due to line ending changes in `THIRD-PARTY-NOTICES.txt`.

Update `xaprepare` to always normalize line endings to
`Environment.NewLine` in `THIRD-PARTY-NOTICES.txt` to prevent
this issue.

Additionally, these scenarios where the build unintentionally
modifies git tracked files on some platforms are frustrating, so
let's prevent them from happening in the first place.

Add a CI check to fail a build if any git tracked files were modified.

Example:

> ❌ **git gree has modified tracked files.**

![image](https://github.com/user-attachments/assets/ec8869f5-75a5-4234-b7f4-20c2cabd743e)

Clicking the error will show the modified file(s):

>     "C:\Windows\System32\WindowsPowerShell\v1.0\powershell.exe" -NoLogo -NoProfile -NonInte…
>     HEAD detached at b1a5f77
>     Changes not staged for commit:
>       (use "git add ‹file›..." to update what will be committed)
>       (use "git restore ‹file›..." to discard changes in working directory)
>            modified:  THIRD-PARTY-NOTICES. TXT
>     …
>     ##[error]git tree has modified tracked files.

![image](https://github.com/user-attachments/assets/395ee30e-8a37-450c-94ec-106221c40db3)

build-tools/automation/yaml-templates/build-linux.yaml

@@ -104,4 +104,8 @@ stages:
         includeBuildResults: true
         use1ESTemplate: ${{ parameters.use1ESTemplate }}
 
+    - template: /build-tools/automation/yaml-templates/fail-on-dirty-tree.yaml
+      parameters:
+        xaSourcePath: $(System.DefaultWorkingDirectory)/xamarin-android
+
     - template: /build-tools/automation/yaml-templates/fail-on-issue.yaml

build-tools/automation/yaml-templates/build-macos.yaml

@@ -86,3 +86,7 @@ stages:
         artifactName: ${{ parameters.buildResultArtifactName }}
         includeBuildResults: true
         use1ESTemplate: ${{ parameters.use1ESTemplate }}
+
+    - template: /build-tools/automation/yaml-templates/fail-on-dirty-tree.yaml
+      parameters:
+        xaSourcePath: ${{ parameters.xaSourcePath }}

build-tools/automation/yaml-templates/build-windows.yaml

@@ -117,4 +117,6 @@ stages:
         artifactName: ${{ parameters.buildResultArtifactName }}
         includeBuildResults: true
 
+    - template: /build-tools/automation/yaml-templates/fail-on-dirty-tree.yaml
+
     - template: /build-tools/automation/yaml-templates/fail-on-issue.yaml

build-tools/automation/yaml-templates/fail-on-dirty-tree.yaml

@@ -0,0 +1,22 @@
+# Ensure the build did not produce any modified checked in files
+
+parameters:
+  condition: succeeded()
+  xaSourcePath: 
+
+steps:
+- powershell: |
+    # Run this to log the output for the user
+    git status
+
+    # Run this to error the build if untracked files
+    $process= git status --porcelain --untracked-files=no
+
+    if ($process)
+    {
+        Write-Host "##vso[task.logissue type=error]git tree has modified tracked files."
+        Write-Host "##vso[task.complete result=Failed;]"
+    }
+  displayName: Ensure no modified committed files
+  workingDirectory: ${{ parameters.xaSourcePath }}
+  condition: ${{ parameters.condition }}

build-tools/xaprepare/xaprepare/Steps/Step_ThirdPartyNotices.cs

@@ -151,7 +151,7 @@ string FetchTPNLicense (string relativeFilePath)
 			if (!File.Exists (path))
 				throw new InvalidOperationException ($"License file {path} does not exist");
 
-			return File.ReadAllText (path);
+			return File.ReadAllText (path).ReplaceLineEndings ();
 		}
 
 		void EnsureValidTPNType (Type type)