Fix possible orphaned proto_library targets

This is a fix for aosp/2693190 that handled .proto files that end up in
different bazel packages. It did it by creating proto_library targets in
the correct bazel package.

Changing the granularity causes issues if the the new proto_library in
the subpackage imports a .proto file from a parent package or a
different package. e.g.
```
tmp
├── foo.proto
└── subdir/import_foo.proto # contains an `import "foo.proto"`
└── subdir/Android.bp # package boundary
├── Android.bp # contains a cc_library with foo.proto and
# subdir/import_foo.proto
```

At ToT, the ProtoInfo we provide to CcProtoGen is correct, but the
proto_library in subdir/BUILD will not compile because it does not have
a dep on the proto_library in ./BUILD

This CL creates a workaround by adding `manual` to the proto_library
targets. This CL is based on the assumption that the buildable unit in
bp2build is cc_library_*, and not proto_library necessarily (atleast
till we do a manual/automated cleanup)

Test: Created an integration test in build/bazel
Test: go test ./bp2build
Bug: 292583584
Bug: 246997908
Change-Id: I73120be2411967cb144f37ed4417f76ecf1a6ffa

android/proto.go

@@ -283,6 +283,15 @@ func Bp2buildProtoProperties(ctx Bp2buildMutatorContext, m *ModuleBase, srcs baz
 				}
 			}
 
+			// TODO - b/246997908: Handle potential orphaned proto_library targets
+			// To create proto_library targets in the same package, we split the .proto files
+			// This means that if a proto_library in a subpackage imports another proto_library from the parent package
+			// (or a different subpackage), it will not find it.
+			// The CcProtoGen action itself runs fine because we construct the correct ProtoInfo,
+			// but the FileDescriptorSet of each proto_library might not be compile-able
+			if pkg != ctx.ModuleDir() {
+				tags.Append(bazel.MakeStringListAttribute([]string{"manual"}))
+			}
 			ctx.CreateBazelTargetModule(
 				bazel.BazelTargetModuleProperties{Rule_class: "proto_library"},
 				CommonAttributes{Name: name, Dir: proptools.StringPtr(pkg), Tags: tags},

bp2build/cc_library_conversion_test.go

@@ -4967,6 +4967,7 @@ cc_library_static {
 	tc.ExpectedBazelTargets = []string{
 		MakeBazelTarget("proto_library", "foo_proto", AttrNameToString{
 			"srcs": `["//bar:bar.proto"]`,
+			"tags": `["manual"]`,
 		}),
 	}
 	runCcLibraryTestCase(t, tc)
@@ -4976,6 +4977,7 @@ cc_library_static {
 	tc.ExpectedBazelTargets = []string{
 		MakeBazelTarget("proto_library", "foo_proto", AttrNameToString{
 			"srcs": `["//baz/subbaz:baz.proto"]`,
+			"tags": `["manual"]`,
 		}),
 	}
 	runCcLibraryTestCase(t, tc)
@@ -5035,6 +5037,7 @@ cc_library_static {
 			"srcs":                `["//bar:bar.proto"]`,
 			"strip_import_prefix": `""`,
 			"import_prefix":       `"bar"`,
+			"tags":                `["manual"]`,
 		}),
 	}
 	runCcLibraryTestCase(t, tc)
@@ -5046,6 +5049,7 @@ cc_library_static {
 			"srcs":                `["//baz/subbaz:baz.proto"]`,
 			"strip_import_prefix": `""`,
 			"import_prefix":       `"baz/subbaz"`,
+			"tags":                `["manual"]`,
 		}),
 	}
 	runCcLibraryTestCase(t, tc)