Simplify key-based thread locals
This PR simplifies key-based thread-locals by:
* unifying the macro expansion of `const` and non-`const` initializers
* reducing the amount of code in the expansion
* simply reallocating on recursive initialization instead of going through `LazyKeyInner`
* replacing `catch_unwind` with the shared `abort_on_dtor_unwind`
It does not change the initialization behaviour described in #110897.
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