Make room-testing a KMP project

Also removed the single AutoMigration test in the project as that is already covered by multiple other tests in the integration test projects. By removing the test we avoid applying KSP to the project and thus saving a bit of build time. Infra will be happy... :)

Bug: 299168035
Test: ./gradlew :room:room-testing:build
Change-Id: I953908b1227b83df859a2c305ecc7e5481b558ae
diff --git a/docs-tip-of-tree/build.gradle b/docs-tip-of-tree/build.gradle
index ea1a9dd..e9596b8 100644
--- a/docs-tip-of-tree/build.gradle
+++ b/docs-tip-of-tree/build.gradle
@@ -333,7 +333,7 @@
     kmpDocs(project(":room:room-runtime"))
     docs(project(":room:room-rxjava2"))
     docs(project(":room:room-rxjava3"))
-    docs(project(":room:room-testing"))
+    kmpDocs(project(":room:room-testing"))
     docs(project(":safeparcel:safeparcel"))
     docs(project(":savedstate:savedstate"))
     docs(project(":savedstate:savedstate-ktx"))