Use genrule to pull in bindgen-erated source

Rather than having a local modification of the upstream Rust source,
instead use a genrule to replace the `${INCLUDES}` placeholder with
a re-export of everything from the bindgen-created code.

This change means that the upstream BoringSSL source no longer has a
local modification, making it easier to import new versions.

Also add a rust_test for the bindgen layout tests along the way.

Bug: 177080016
Test: build targets, atest libbssl_sys_raw_test
Change-Id: Iabf1b6ac4ae7d3a391cc038b29f157347fb36f2f
Merged-In: Iabf1b6ac4ae7d3a391cc038b29f157347fb36f2f
(cherry picked from commit 71257a0a0347296eba49f1ca39c0e6b024243ffb)
(cherry picked from commit 1364953c681d19461b5bf3f291cc336c1ec0f625)
Merged-In: Iabf1b6ac4ae7d3a391cc038b29f157347fb36f2f
3 files changed