Add module bcr.x version identifiers to modules

[aaronmondal]

At eomii we have our own registry for rules_ll dependencies to avoid clashes with rules_cc. We just released a new rules_ll version that breaks the previous API and found an issue that the BCR might run into in the future.

If we update all modules to use the new API we would break the builds of anyone using the older API. To avoid this issue in the future we've decided on adding -bcr.x identifiers to module versions. This way we can have e.g. ll_asio version 1.24.0-bcr.0 and 1.24.0-bcr.1 coexist for users of both APIs.

This scheme was originally proposed by @Wyverald in #205 (comment). I think it could be a nice idea to use this scheme or a similar one for the BCR in general.

It may be even better if a single module could have compatibility modes for different toolchain versions. As far as I understand, the current compatibility_level doesn't let us do this. Or maybe I'm wrong here and there is such a possibility already?