Handle ambiguous headers in BCR

[mateusz-olczyk]

Fixes #173

New index.DependencyIndex type is now applied everywhere. Type ccDependencyIndex has been dropped.

This review is not so huge; most of the lines come from the new bzldep-index.json.

Warning

I needed to turn off WithAmbiguousTargetsResolved() call in BCR indexer. For some reason, the algorithm resolves "grpcpp/grpcpp.h" only to "@grpc//:grpc++_codegen_proto", which is incorrect.

bazel query 'somepath(":grpc++_codegen_proto", ":grpc++")' returns empty result, which is bad, because :grpc++ contains the crucial compiled code.

I guess the function GroupTargetsByHeaders() is not the right strategy for solving conflicts, because it groups targets if they intersect with at least one header in their "hdrs" lists - whatever it is.

Instead of grouping targets like this, we should consider the mapping from each recognized header to its parent targets. And then resolve conflicts in such defined groups of targets. This way, each header is treated separately.

[jayconrod]

This is showing as +178,752 −32,736, too much to review. Can you split the update of bzldep-index.json into a separate PR? Then I can review that part by re-running the tool and verifying it produces the same output.

[mateusz-olczyk]

This is showing as +178,752 −32,736, too much to review. Can you split the update of bzldep-index.json into a separate PR? Then I can review that part by re-running the tool and verifying it produces the same output.

Sure, I'll do that later. For now, I've converted it to a draft, because a new problem appeared: #184