Add ASCII-related methods from u8 and MIN/MAX to core::ascii::Char

[ChaiTRex]

• Add ASCII-related methods from u8 to core::ascii::Char.
• Add core::ascii::Char::MIN and core::ascii::Char::MAX.

Tracking issue #110998.

Can someone please ping @rust-lang/libs-api? These additions were not in the original ACP (rust-lang/libs-team#179).

[rustbot]

r? @ibraheemdev

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[ibraheemdev]

r? libs-api

[tgross35]

Suggested an ACP on Zulip. A few notes

• I don't know if we need to exactly replicate naming from char/u8 here. E.g. I think the compact and non-redundant names to_uppercase and is_digit outweighs consistency with to_ascii_uppercase and is_ascii_digit.
• Similarly, I don't know when is_ascii would be needed except for somebody migrating from char/u8 to AsciiChar. In which case, they should remove whatever they're doing with the check rather than accidentally using this.
• All of these could take self/Self rather than &self/&Self since it's Copy (and trivially so). Arguably it should have been the same for u8 and char, not sure what to do with consistency here.

[tgross35]

ACP was accepted with changes, for that:
@rustbot author

r? tgross35

[rustbot]

Reminder, once the PR becomes ready for a review, use @rustbot ready.

[rustbot]

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