A few more regex test

[danmoseley]

Borrow a few parser tests from Rust (https://github.com/rust-lang/regex). I'll add some execution tests later, although unfortunately many we already have as they derive from the AT&T tests.

Work around #56945 which only seems to affect one of my machines.

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Issue Details

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Borrow a few parser tests from Rust (https://github.com/rust-lang/regex). I'll add some execution tests later, although unfortunately many we already have as they derive from the AT&T tests.

Work around #56945 which only seems to affect one of my machines.

Author:	danmoseley
Assignees:	-
Labels:	area-System.Text.RegularExpressions
Milestone:	-

[pgovind]

Nothing more to add after Stephen's comments. LGTM!

[danmoseley]

@steveisok I have seen this MacCatalyst was canceled on other PR's.

I'm merging because the possibility of these test changes having an issue specific to MacCatalyst is ~zero.