swift234

[SE-0081] Warn on deprecated where clause inside angle brackets

and provide a fix-it to move it to the new location as referenced
in SE-0081.

Fix up a few stray places in the standard library that is still using
the old syntax.

Update any ./test files that aren't expecting the new warning/fix-it
in -verify mode.

While investigating what I thought was a new crash due to this new
diagnostic, I discovered two sources of quite a few compiler crashers
related to unterminated generic parameter lists, where the right
angle bracket source location was getting unconditionally set to
the current token, even though it wasn't actually a '>'.