ci: move public-api goldens to goldens directory (#35768)

Moves the public api .d.ts files from tools/public_api_guard to
goldens/public-api.

Additionally, provides a README in the goldens directory and a script
assist in testing the current state of the repo against the goldens as
well as a command for accepting all changes to the goldens in a single
command.

PR Close #35768

packages/platform-browser/BUILD.bazel

@@ -1,4 +1,4 @@
-load("//tools:defaults.bzl", "ng_module", "ng_package")
+load("//tools:defaults.bzl", "ng_module", "ng_package", "ts_api_guardian_test_npm_package")
 
 package(default_visibility = ["//visibility:public"])
 
@@ -43,3 +43,13 @@ ng_package(
         "//packages/platform-browser/testing",
     ],
 )
+
+ts_api_guardian_test_npm_package(
+    name = "platform-browser_api",
+    actualDir = "packages/platform-browser/npm_package",
+    data = [
+        ":npm_package",
+        "//goldens:public-api",
+    ],
+    goldenDir = "goldens/public-api/platform-browser",
+)