* 'super' in a overriding decl is "common".
* type decl introducers (e.g. 'struct', 'enum') at top-level in library
files are "common"
* type decl introducers in 'protocol' are invalid, hence "rare"
* top-level only decl introducer (e.g. 'import', 'extension') are invalid
at non-top-level, hence "rare"
* nested types in function bodies are "rare"
* member only decls (e.g. 'subscript', 'deinit') are invalid in function
body, hence "rare"
* some modifiers (e.g. 'public', 'private', 'override') are invalid for
local decls, hence "rare"
rdar://77934651
The Python build system always enables concurrency, but CMake has it
disable by default. Collaborators that do not use the Python build
system and use directly CMake will have it disable, unless they
explicitely enable it. If the tests are not marked as requiring the
concurrency features, the tests will fail to execute when concurrency is
disabled.
The changes add the `REQUIRES: concurrency` line to many tests that deal
with concurrency, but wasn't marked as such.
