Escape additonal classes of characters in escape_debug_ext

[Jules-Bertholet]

(See also #158057, #155527)

This PR escapes a few additional categories of characters in escape_debug_ext (used to implement char::escape_debug and the various Debug impls for characters and strings):

• Deprecated characters: Unicode says that the use of these characters is "strongly discouraged".
• Full composition exclusion characters: These characters cannot occur in strings normalized according to any of the Unicode normalization forms. Any string containing one of these characters is necessarily unnormalized.
• NFC_Quick_Check=Maybe characters: Depending on context, these characters may sometimes appear in NFC-normalized text, or they may be removed by the application of NFC. Most characters in this category are also grapheme extenders, which we already escape, but there are a few that are not. By escaping these last as well, we ensure that any string which is not normalized according to NFC gets escaped; that seems useful for debugging normalization-related issues. (Note: NFC_Quick_Check=No is equivalent to Full_Composition_Exclusion=Yes.)

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Additionally, the second commit makes the Deprecated and Full_Composition_Exclusion data tables unstably public, behind the unicode_discouraged feature gate, so that users don't need to ship duplicate copies of std data tables. Libs-api can feel free to reject if unsure.

Making the NFC_Quick_Check=Maybe table public is left to future work, because the API for that is more complicated (quick_check returns a 3-valued enum instead of a boolean, do we want to ship more normalization data alongside it, etc.). However, we do leave room for it by including the whole table, instead of optimizing the implementation by including only the diff from Grapheme_Extend.

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Adds 403 bytes total to the Unicode data tables.

@rustbot label A-Unicode T-libs-api needs-fcp

[rustbot]

library/core/src/unicode/unicode_data.rs is generated by the src/tools/unicode-table-generator tool.

If you want to modify unicode_data.rs, please modify the tool then regenerate the library source file via ./x run src/tools/unicode-table-generator instead of editing unicode_data.rs manually.

[rustbot]

r? @Darksonn

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[Darksonn]

Is this intended to supersede #158057, or be merged before/after that one?

[Jules-Bertholet]

Is this intended to supersede #158057, or be merged before/after that one?

They are conceptually independent changes—that PR removes some characters from the list we escape, this PR adds some. I'll need to rebase in between them, though.