build(core): add bazel test targets for core (#21053)

- Add tests target for `test`, `test_node_only` and `test_web` in `core` package.
- Created a `_testing_init` pseudo package where bootstrap code for tests is kept.
- Moved `source_map_util` from `test` to `testing` so to prevent circular dependency.
- Removed `visibility:public` for testing `BUILD` packages.

PR Close #21053

WORKSPACE

@@ -16,12 +16,12 @@ node_repositories(package_json = ["//:package.json"])
 git_repository(
     name = "build_bazel_rules_typescript",
     remote = "https://github.com/bazelbuild/rules_typescript.git",
-    tag = "0.6.0",
+    tag = "0.7.1",
 )
 
-load("@build_bazel_rules_typescript//:defs.bzl", "ts_repositories")
+load("@build_bazel_rules_typescript//:setup.bzl", "ts_setup_workspace")
 
-ts_repositories()
+ts_setup_workspace()
 
 local_repository(
     name = "angular",