Auto merge of #150844 - fmease:mv-ace-tests, r=BoxyUwU

mGCA: Move tests for assoc const bindings (formerly ACE) into dedicated directory & replace more mentions of ACE

Split out of PR rust-lang/rust#150843.
As discussed.

Somewhat obvious underlying principle: If the test checks basic or core parts of assoc const bindings and nothing else, move it, otherwise leave it even if it contains ACEs.

Motivation: It makes a lot easier for me to continue working on ACE efficiently.

r? @BoxyUwU

Author: bors