Leading Unicode escapes and surrogate pair escapes are not parsed in RegExp group names

[graphemecluster]

🔎 Search Terms

• Unicode escape sequences
• extended Unicode escapes, surrogate escapes
• regular expression group names, regex identifiers
• bundling & transpilation

🕗 Version & Regression Information

• This is the behavior since Provide Syntax Checking for Regular Expressions #55600 lands

⏯ Playground Link

https://www.typescriptlang.org/play/?target=99#code/PQCg-APAhgOgrgBgQNgIwD4CUMDW15Jrq7RTrBwDcAUKJAShtng0SWRTXfnAN6oBmJAgC+WdvH5CkY9oBgNwAA75KrXARJg4WObq+mmcTyLlXNfAAiADgQBhCzaTiWcK7fuOSxzqsiwX1uxcHBCceV0DzYMNoLxUgA

💻 Code

/(?<a\u0061>)\k<a\u0061>\k<aa>/u;             // Correct parsed
/(?<\u0061>)\k<\u0061>\k<a>/u;                // TS1514: Expected a capturing group name.
/(?<a\u{13000}>)\k<a\u{13000}>\k<a𓀀>/u;       // Correct parsed
/(?<\u{13000}>)\k<\u{13000}>\k<𓀀>/u;          // TS1514: Expected a capturing group name.
/(?<\uD80C\uDC00>)\k<\uD80C\uDC00>\k<𓀀>/u;    // TS1514: Expected a capturing group name.
/(?<a\uD80C\uDC00>)\k<a\uD80C\uDC00>\k<a𓀀>/u; // TS1005: '>' expected.

🙁 Actual behavior

Errors are emitted at the start of Unicode escapes, extended Unicode escapes or surrogate pair escapes of 4 of the lines above.

🙂 Expected behavior

All group names are correctly parsed and normalised, and no errors are emitted.

Additional information about the issue

Fixed in #63996, this issue is opened only for trackability and bookkeeping purpose.