Add Tests Submodules

.gitmodules

 [submodule "ShaderGraph"]
 	path = ShaderGraph
 	url = https://github.com/Unity-Technologies/ShaderGraph
+[submodule "Tests/UTF_Core"]
+	path = Tests/UTF_Core
+	url = git@github.com:Unity-Technologies/UTF_Core.git
+[submodule "Tests/UTF_HDRP"]
+	path = Tests/UTF_HDRP
+	url = git@github.com:Unity-Technologies/UTF_Tests_HDRP.git

Tests/UTF_Core.meta

+fileFormatVersion: 2
+guid: b453f6a18bedf6f4da636bfee9a127c1
+folderAsset: yes
+DefaultImporter:
+  externalObjects: {}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 

Tests/UTF_HDRP.meta

+fileFormatVersion: 2
+guid: 86137e24adbf2b7488553f8ddda7cc8e
+folderAsset: yes
+DefaultImporter:
+  externalObjects: {}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: