Add deprecation warning for base-rules-hook

This lets product/board config define a function that
is called while processing modules defined in an
Android.mk file.

When the product/board configs are converted
to starlark, they won't be able to supply a base-rules-hook
anymore. Emit a warning saying that it's deprecated.

Bug: 226974242
Test: Manually
Change-Id: Ie6baa4952516a3ec5c6c440f9106f7b5185803b7