Update buildSrc srcDirs for androidx-plugin build
Update buildSrc srcDirs for androidx-plugin build

androidx-plugin is the way buildSrc is built for Playground builds. This
CL updates the androidx-plugin wrapper projects to the new srcDir
structure in buildSrc

Test: cd androidx-plugin && ./gradlew gradle-plugin:assemble
Change-Id: Idd4f5fed88662a5354276b041d587143ceb1dc81

AndroidX/androidx,AndroidX/androidx,AndroidX/androidx,AndroidX/androidx,androidx/androidx,androidx/androidx,AndroidX/androidx,AndroidX/androidx,androidx/androidx,AndroidX/androidx,AndroidX/androidx,androidx/androidx,AndroidX/androidx,androidx/androidx,androidx/androidx,androidx/androidx,androidx/androidx,AndroidX/androidx,androidx/androidx,androidx/androidx