Auto merge of #51859 - kennytm:rollup, r=kennytm

Rollup of 7 pull requests

Successful merges:

 - #49987 (Add str::split_ascii_whitespace.)
 - #50342 (Document round-off error in `.mod_euc()`-method, see issue #50179)
 - #51658 (Only do sanity check with debug assertions on)
 - #51799 (Lower case some feature gate error messages)
 - #51800 (Add a compiletest header for edition)
 - #51824 (Fix the error reference for LocalKey::try_with)
 - #51842 (Document that Layout::from_size_align does not allow align=0)

Failed merges:

r? @ghost