Multi-tree API bp2build converter for ndk_library

This is a partial bp2build conversion that only emits the
cc_api_contribution target of ndk_library. We also need to convert this
to cc_stub_suite eventually to enable building vendor/product API
domains with Bazel

Also create an enum for the three known Multi-tree API surfaces (will
likely be expanded in the future)

Test: go test ./bp2build
Test: b cquery //bionic/libc:libc.ndk.contribution --output=starlark
--starlark:expr="providers(target)"

Change-Id: Idb24871ba20aae132b61eb31ef35c917cacae9e1
diff --git a/cc/cc.go b/cc/cc.go
index d42ab6d..1c845f6 100644
--- a/cc/cc.go
+++ b/cc/cc.go
@@ -3650,6 +3650,7 @@
 	sharedLibrary
 	headerLibrary
 	testBin // testBinary already declared
+	ndkLibrary
 )
 
 func (c *Module) typ() moduleType {
@@ -3686,6 +3687,8 @@
 			return staticLibrary
 		}
 		return sharedLibrary
+	} else if c.isNDKStubLibrary() {
+		return ndkLibrary
 	}
 	return unknownType
 }
@@ -3726,6 +3729,8 @@
 		} else {
 			sharedOrStaticLibraryBp2Build(ctx, c, false)
 		}
+	case ndkLibrary:
+		ndkLibraryBp2build(ctx, c)
 	}
 }