Experimental feature: Fix some bugs in C++ templates + some enhancements to core

[lordfanger]

Improved extensibility to allow look for surrounding of braces.

• Wrapped running matching logic to class MatchingContext usable in PairBuilder
• Allowed AllowanceResolver to return builders specific only to his file.

Updated C++ template feature to guess whether '<' or '>' is part of template based on their surrounding.

[1821746019]

@madskristensen I cannot wait to try the new version. Could you merge it as fast as possible?

[madskristensen]

Is this ready to merge or still WIP?

[lordfanger]

Ah, sorry. It is ready to merge. :) But still opt-out with experimental flag.

[madskristensen]

Thanks