[HostStubGen] Support experimental APIs

We would like to be able to "toggle" certain APIs at runtime. To achieve
this, we inject a method call hook into the experimental API method
body, and in the method call hook, we can implement whatever logic that
is necessary to determine whether the API should throw or not.

The implementation basically reuses the existing method call hook
infrastructure, but instead of applying it on every single method, the
method call hook can be explicitly set on package/class/method level in
text policy files.

Bug: 292141694
Flag: EXEMPT host side change only
Test: f/b/r/scripts/run-ravenwood-tests.sh
Change-Id: I69036be5bf028fd9e002c3ac7c4db77c613cf172