feat: add PHP mb_strimwidth (AOT + Magician)

[nahime0]

Adds PHP mb_strimwidth() for AOT and Magician/eval, matching PHP 8.5 UTF-8 display-width trim semantics. Needed for Termwind truncate/trimText.

Behavior

mb_strimwidth(string $string, int $start, int $width, string $trim_marker = "", ?string $encoding = null): string

• Omitted/null/UTF-8/UTF8 trim by PHP 8.5 East Asian Width (width 2 in the eaw_table.h ranges, otherwise 1).
• 8bit/binary/7bit treat every byte as width 1.
• $start is a character offset; negative values count from the end.
• If the remaining suffix is wider than $width, it is cut and $trim_marker is appended. When the marker is at least as wide as the budget, PHP returns the marker alone.
• Unknown encodings and out-of-range $start/$width raise catchable ValueError.
• Scope is only mb_strimwidth (not mb_strwidth or other mb_*).

Implementation

• Shared catalog contract + AOT builtin! home.
• Magician eval_builtin! with the same EAW table and trim algorithm.
• Typed RuntimeFnId::MbStrimwidth → __rt_mb_strimwidth for AArch64 and x86_64.
• No iconv / no new runtime-feature bit: unused programs can still strip the helper.

Tests

• Codegen: ASCII/CJK trim, encodings, first-class callable, namespaced lookup, ValueErrors.
• Eval parity through Magician.
• Compile-time arity and type errors.

Docs

• docs/php/strings.md, examples/string-ops, ROADMAP.md, generated builtin pages.

  

[greptile-apps]

Too many files changed for review (279 files, 100 file limit).

Bypass the limit by tagging @greptile-apps to review.

[nahime0]

Superseded by #952, which centralizes the mbstring implementation across the shared contract, AOT, Magician/eval, supported targets, tests, examples, and generated documentation. Closing this standalone PR in favor of #952.