[GR-28711] Implement context independent method lookup

[graalvmbot]

See Jira issue.

[chrisseaton]

See Jira issue.

We can't!

[eregon]

The mirroring simply copies the description from the PR.

In short, there is a SharedIndicesMap per class, and that SharedIndicesMap is shared for corresponding classes (e.g., by where they are defined first, e.g. a class Foo; end) between contexts. A bit like a Shape, but it grows in-place without needing a new instance. So then method lookup is: get the class, check the SharedIndicesMap of that class is the one we expect in the inline cache, if so use the cached index to read from the array of methods (vtable) and lookup is done. In practice, more things are needed like visibility checks, etc in multi-contexts. The additional complexity lies in those arrays of methods (1 per RubyClass instance) being up-to-date with redefinitions anywhere in the hierarchy, but we kind of already handle that since https://medium.com/graalvm/precise-method-and-constant-invalidation-in-truffleruby-4dd56c6bac1a.

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[eregon]

This would be nice for context-independent code, but since that's not a priority currently and it seems tricky to rebase I think best to close for now.