Fix Text truncation at NULL character on iOS and Android (#24129)

[kulkarni-rohan]

Fixes #24129

Summary:

Problem: <Text>{'Hello \u0000 World'}</Text> renders as "Hello" (truncated at \u0000). Does NOT reproduce when Debug JS Remotely (JSON preserves \u0000), but reproduces in production Hermes+Fabric on iOS and Android.

Root cause: JS String preserves \u0000 (length includes it), C++ std::string from JSI utf8() also preserves via size. Truncation happens at platform bridge where C-string NUL-terminated APIs are used:

• iOS: RCTAttributedTextUtils.mm:420 stringWithUTF8String:fragment.string.c_str() stops at embedded \0
• iOS: RCTConversions.h RCTNSStringFromString via stringWithCString: and reverse std::string{UTF8String}
• iOS: RCTTurboModule.mm convertJSIStringToNSString same
• Android: JavaTurboModule.cpp NewStringUTF(c_str()) expects NUL-terminated

Fix (4 files, ~10 lines, no new API): Replace C-string APIs with length-aware [[NSString alloc] initWithBytes:data length:size encoding:NSUTF8StringEncoding] (same as existing correct pattern in FollyConvert.mm:31 and MapBufferBuilder.cpp) and Android convertUTF8ToUTF16 + NewString(jchar*, len) + assign(jsChars, GetStringUTFLength()). All surfaces (Text, TextInput, accessibility, TurboModule params) fixed at once because shared converters are fixed.

Changelog:

[GENERAL] [FIXED] - Fix Text truncation when string contains NULL character \u0000 (#24129)

Test Plan:

Reproduction (RNTester):

• Add screen Text > NullCharacter with {'Hello\u0000World'} and 'A\u0000B\u0000C'
• Before: "Hello" truncated
• After: "HelloWorld" full (invisible \0 zero-width but World visible, length preserved)

Commands:

yarn lint
# → Done (max-warnings 0)

# Text itest requires buck, but JS unit for length preservation:
node -p "'a\u0000b'.length" # → 3

Closes #24129

[meta-codesync]

@fabriziocucci has imported this pull request. If you are a Meta employee, you can view this in D115707536.

[meta-codesync]

@fabriziocucci merged this pull request in 5906cfb.