Add compatibility checking for specs across contexts when grammars are activated

[LexiconCode]

Currently the CCR merge process checks compatibility when adding a grammar. This would go one step further and check all grammars merger and mapping when activated.

Describe the solution you'd like
Imagine for a moment two contexts Navigation and Firefox.

Navigation has a command.
`next tab": R(Key("c-tab")) * Repeat(extra="n"),

Firefox has a command
`next tab": R(Key("c-t")) * Repeat(extra="n"),

They share the same spec but have different actions. if there was compatibility checking at grammar should always win if a global grammar has an identical spec.

This will make it easy to be consistent across all grammars without worrying about spec conflicts.

Describe alternatives you've considered
ContextAction could be used but it becomes cumbersome with two or three applications. I think it's use case is better for edge cases.

I'm currently not sure how this could be implemented but it's worth having documented in an issue.