[5.1] Replace all 9999 availability in non-stdlib tests. (#26109) (#26145)
* Replace all 9999 availability in non-stdlib tests. (#26109)
Replace all 9999 availability in non-stdlib tests with the appropriate platform availability.
* Merge pull request #26129 from aschwaighofer/fix_test_dynamic_replacement_opaque_result
Fix test/Interpreter/dynamic_replacement_opaque_result.swift