ICU-23314 UnicodeSet: extended name escapes

[aryanraj45]

Implements support for extended name escapes in UnicodeSet patterns as specified in ICU-23314.

Changes

This PR adds support for the \N{hex:name} syntax in UnicodeSet patterns, allowing users to specify both the hexadecimal code point and its Unicode name for validation purposes.

Implementation Details

• Extended the applyPropertyPattern() method in UnicodeSet.java to parse the new hex:name format
• When a colon is detected in \N{...}, the format is parsed as hex:name
• The hex value is parsed and validated to be a valid code point (0-0x10FFFF)
• The actual Unicode name is retrieved and compared with the provided name
• If names don't match, an IllegalArgumentException is thrown
• Backward compatibility maintained: standard \N{name} syntax continues to work

Testing

• Added comprehensive test cases in UnicodeSetTest.TestExtendedNameEscapes()
• Tests cover: valid hex:name format, name mismatch errors, invalid hex errors, out-of-range errors, and backward compatibility
• All existing UnicodeSet tests (55 tests) continue to pass

Example Usage

// Valid usage
UnicodeSet set = new UnicodeSet("[\\N{0041:LATIN CAPITAL LETTER A}]"); // Works
UnicodeSet emoji = new UnicodeSet("[\\N{1F4A9:PILE OF POO}]"); // Works

// Invalid usage - throws exception
UnicodeSet invalid = new UnicodeSet("[\\N{0041:WRONG NAME}]"); // Error: name mismatch

###Checklist

• Required: Issue filed: ICU-23314
• Required: The PR title must be prefixed with a JIRA Issue number. Example: "ICU-NNNNN Fix xyz"
• Required: Each commit message must be prefixed with a JIRA Issue number. Example: "ICU-NNNNN Fix xyz"
• Issue accepted (done by Technical Committee after discussion)
• Tests included, if applicable
• API docs and/or User Guide docs changed or added, if applicable
• Approver: Feel free to merge on my behalf

[eggrobin]

As noted on JIRA, this PR is moot, but since I am looking at it: This isn’t for backward compatibility; these just serve different purposes. Sometimes you just want to refer to the character LATIN CAPITAL LETTER A and you don’t actually care what the code point is; the name alone is more readable.

In other cases, you care about the code point (what motivated that is tooling used to develop the Unicode Character Database; for new characters we absolutely want to check that we are putting them in the right place).

Likewise for the hex:literal:name version: sometimes you might want to illustrate what the character is, other times you might not need to (or it might be impractical, e.g., for control characters.

[aryanraj45]

Thanks for the explanation! I understand now since the parser is being rewritten, my changes would conflict with that work.

I appreciate you taking the time to review and explain the context. I'll close this PR and look for other issues where I can contribute more effectively.

Sorry for not catching this earlier!