Use unix line endings always, even on Windows (#24817)

- Fixes #24791
- Fixes #24790
- Ensures developers can successfully work on both Linux and Windows
- Consistent with other repos like `microsoft/typespec` and `azure/azure-sdk-for-js`
- Required for node-based tools like `tsp format` which assume LF

.gitattributes

@@ -1,2 +1,2 @@
-# Set the default behavior, in case people don't have core.autocrlf set.
-* text=auto
+# Use unix line endings always, even on Windows
+* text=auto eol=lf

eng/pipelines/typespec-validation-all.yml

@@ -8,9 +8,19 @@ pr: none
 
 jobs:
 - job: Validate_All_Specs
+
+  strategy:
+    matrix:
+      Linux:
+        Pool: azsdk-pool-mms-ubuntu-2204-general
+        OsVmImage: ubuntu-22.04
+      Windows:
+        Pool: azsdk-pool-mms-win-2022-general
+        OsVmImage: windows-2022
+
   pool:
-    name: azsdk-pool-mms-ubuntu-2204-general
-    vmImage: ubuntu-22.04
+    name: $(Pool)
+    vmImage: $(OSVmImage)
 
   steps:
   - script: npm ci