Move framework proto build rules to separate file

The proto build rules are quite large and makes the top-level Android.bp
file difficult to navigate. Move them to a separate file.

Bug: 185128417
Test: m
Merged-In: I5719ba0fa8e03dcfca0cc32dc30db3f87ea4e3cd
Change-Id: I5719ba0fa8e03dcfca0cc32dc30db3f87ea4e3cd
diff --git a/OWNERS b/OWNERS
index 710f13e..4970dd1 100644
--- a/OWNERS
+++ b/OWNERS
@@ -30,3 +30,4 @@
 per-file Android.mk = file:platform/build/soong:/OWNERS
 per-file ApiDocs.bp = file:platform/build/soong:/OWNERS
 per-file StubLibraries.bp = file:platform/build/soong:/OWNERS
+per-file ProtoLibraries.bp = file:platform/build/soong:/OWNERS