Initial commit of "HostStubGen" (Ravenwood)

See tools/hoststubgen/README.md for the directory structure...

This CL contains:
- The HostGenTool.

- Libraries to build / run host side tets. (helper-*/ directories)

- Currently we expose ArrayMap and Log to the host side, but we also need to
expose a lot more classes that the tests usee.

- Some sample tests. (test-framework/ and test-tiny-framework/)

Sample tests contain very small tests for ArrayMap and Log.

- This version doen't loa JNI code yet. It still uses the Java substitution
for Log's native methods.

This is because `libandroid_runtime` seems to have a lot of obscure dependencies,
and using `libandroid_runtime` could cause obscure build errors when someone
make chages to any of direct/indirect dependencies.

- Current version doesn't use any Java annotations to control what are exposed
on the host side. Instead, we use `framework-policy-override.txt`, which is
easier to change. (because changing the file wouln't require rebuilding
framework-minus-apex.jar.)

- Currently we expose ArrayMap and Log to the host side, but we also need to
expose a lot more classes that the tests usee. See the `framework-policy-override.txt`
file.

Test: ./scripts/run-all-tests.sh
Bug: 292141694
Change-Id: If149e26aa919d17a0b82dacc78f31bd79fbb110b