Split java_lite_grpc_library from java_grpc_library Bazel rule

As discussed in #5237. This is already the direction the rule was going.

Before making the change, I need to get some agreement internally that the benefit outweighs the churn to our users. Otherwise I wouldn't be able to migrate existing usages.

There will need to be a long period where the new rule exists and you can still specify "flavor" for the old behavior, to allow migration.

CC @ceason