Add reflect.Type.ConvertibleTo()

[dgryski]

No description provided.

[dgryski]

There's a bunch more conversions that are still stubbed, but this one was commented out and easy enough to handle.

[dgryski]

Ready for review!

[Copilot]

Pull request overview

Implements reflect.Type.ConvertibleTo (previously a panic stub) by adding a type-level ConvertibleTo method on internal/reflectlite.RawType, and fills in the remaining reflect.Value.Convert machinery (complex, pointer, string↔runes, int/uint→string) needed for the conversion tests. The PR also re-enables a large portion of the upstream convertTests table in reflect/all_test.go, deletes the narrower convert_test.go, exposes test-only IsRO/MakeRO helpers on reflectlite.Value, renames the basic conversion test to TestConvertBasic to avoid colliding with the re-enabled TestConvert, and tweaks runtime.encodeUTF8 to take a rune and widen to uint32 internally.

Changes:

• Implement RawType.ConvertibleTo and wire (reflect.Type).ConvertibleTo through it.
• Flesh out convertOp (complex, pointer, string↔runes) and add cvtComplex/cvtDirect/makeComplex plus real cvtIntString/cvtUintString/cvtStringRunes/cvtRunesString implementations.
• Re-enable large portions of upstream convertTests/TestConvert, expose IsRO/MakeRO, delete convert_test.go, rename old TestConvert → TestConvertBasic, and adjust encodeUTF8 signature.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
src/reflect/type.go	Replace ConvertibleTo panic stub with delegation to RawType.ConvertibleTo.
src/internal/reflectlite/type.go	New RawType.ConvertibleTo covering numeric, slice/string, pointer, identical-underlying, and empty-interface cases (struct/chan TODO).
src/internal/reflectlite/value.go	Add complex/pointer conversion paths, real cvt* string helpers, makeComplex/cvtDirect, and expose IsRO/MakeRO.
src/reflect/all_test.go	Re-enable upstream convertTests and TestConvert, add IsRO/MakeRO helpers; keep struct-tag/channel/interface and slice-panic tests commented out.
src/reflect/convert_test.go	Deleted; numeric coverage subsumed by all_test.go.
src/reflect/value_test.go	Rename existing TestConvert to TestConvertBasic to avoid name collision.
src/runtime/string.go	encodeUTF8 now takes rune and converts to uint32 internally.

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