Handle .proto files in different package for filegroups

Followup to aosp/2693190, this CL adds the support to filegroups.
<mod>__bp2build_converted is now an alias to a proto_library
target <mod>_proto. This proto_library will be created in a different
package if the .proto file exists in a different package.

Test: bp2build unit tests
Test: TH
Bug: 292583584
Change-Id: I8ca452aacf1a86dfc9e218464e38aab89afa5a29
diff --git a/bp2build/cc_library_conversion_test.go b/bp2build/cc_library_conversion_test.go
index 496a482..cac604b 100644
--- a/bp2build/cc_library_conversion_test.go
+++ b/bp2build/cc_library_conversion_test.go
@@ -2434,12 +2434,18 @@
 			}), MakeBazelTarget("cc_library_shared", "a", AttrNameToString{
 				"dynamic_deps":       `[":libprotobuf-cpp-lite"]`,
 				"whole_archive_deps": `[":a_cc_proto_lite"]`,
-			}), MakeBazelTargetNoRestrictions("proto_library", "a_fg_proto_bp2build_converted", AttrNameToString{
+			}), MakeBazelTargetNoRestrictions("proto_library", "a_fg_proto_proto", AttrNameToString{
 				"srcs": `["a_fg.proto"]`,
 				"tags": `[
         "apex_available=//apex_available:anyapex",
         "manual",
     ]`,
+			}), MakeBazelTargetNoRestrictions("alias", "a_fg_proto_bp2build_converted", AttrNameToString{
+				"actual": `"//.:a_fg_proto_proto"`,
+				"tags": `[
+        "apex_available=//apex_available:anyapex",
+        "manual",
+    ]`,
 			}), MakeBazelTargetNoRestrictions("filegroup", "a_fg_proto", AttrNameToString{
 				"srcs": `["a_fg.proto"]`,
 			}),
@@ -2476,12 +2482,18 @@
 			}), MakeBazelTarget("cc_library_shared", "a", AttrNameToString{
 				"dynamic_deps":       `[":libprotobuf-cpp-lite"]`,
 				"whole_archive_deps": `[":a_cc_proto_lite"]`,
-			}), MakeBazelTargetNoRestrictions("proto_library", "a_fg_proto_bp2build_converted", AttrNameToString{
+			}), MakeBazelTargetNoRestrictions("proto_library", "a_fg_proto_proto", AttrNameToString{
 				"srcs": `["a_fg.proto"]`,
 				"tags": `[
         "apex_available=//apex_available:anyapex",
         "manual",
     ]`,
+			}), MakeBazelTargetNoRestrictions("alias", "a_fg_proto_bp2build_converted", AttrNameToString{
+				"actual": `"//.:a_fg_proto_proto"`,
+				"tags": `[
+        "apex_available=//apex_available:anyapex",
+        "manual",
+    ]`,
 			}), MakeBazelTargetNoRestrictions("filegroup", "a_fg_proto", AttrNameToString{
 				"srcs": `["a_fg.proto"]`,
 			}),