metadata-generator/CMakeLists.txt: downgrade two diagnostics from
errors to warnings. Both fire inside LLVM 17.0.6's own headers on
newer Apple toolchains and have no fix on our side:

• -Wunnecessary-virtual-specifier on virtual void anchor() inside
  classes declared final (e.g. clang/AST/Decl.h:151).
• -Wpreferred-type-bitfield-enum-conversion on bitfield-to-enum
  stores in clang AST headers.

The suppressions are guarded by check_cxx_compiler_flag so older
toolchains that don't recognize the flag names skip the
add_compile_options call cleanly.

V8 JSI runtime

NativeScript/v8runtime/V8Runtime.cpp:
evaluatePreparedJavaScript was passing nullptr as the
std::string sourceURL argument. Clang 17's -Wnonnull rejects
implicit conversion from nullptr to the std::string(const char*)
constructor. The function body is unreachable in practice (the sibling
prepareJavaScript already returns nullptr), but it still has to
compile. Switch to "" — the conventional "unknown source URL"
sentinel.

V8 inspector — UChar / char_traits

libc++ in MacOSX26.4.sdk deprecates std::char_traits<T> for any
T other than the standard char family (char, wchar_t,
char8_t, char16_t, char32_t). String16 is backed by
std::basic_string<UChar> with using UChar = uint16_t;, so every
inclusion of <string> after string-16.h instantiates
char_traits<unsigned short> and the whole inspector translation
unit fails under -Werror,-Wdeprecated-declarations.
Switch UChar to char16_t, which makes std::basic_string<UChar>
resolve to the fully supported std::u16string. The V8 inspector
public API surface still passes uint16_t* over its interfaces, so
string-util.h now uses reinterpret_cast at exactly those
boundaries — both directions are bit-identical 16-bit codepoints, so
the cast is sound.
utils.mm::ToStdString previously built a std::vector<uint16_t>
and then copy-constructed a std::u16string from that vector's
iterators. That iterator-range constructor pulled the deprecated
char_traits<unsigned short> back in through the back door. Rewrite
to write char16_t directly into the destination std::u16string,
dropping the intermediate vector.
JsV8InspectorClient.mm: add a file-local Make8BitStringView
helper that builds a StringView over a std::string's storage as
an 8-bit (LATIN1/ASCII) view. Use it at the three sites that
previously inflated each ASCII/UTF-8 JSON byte into a uint16_t,
allocated a std::vector<uint16_t>, and then handed it to the
16-bit StringView constructor. The new path is shorter, allocates
nothing, and no longer touches the deprecated 16-bit string-traits
chain at all.

Summary by CodeRabbit

Release Notes

• Bug Fixes

  • Fixed compilation issues on newer Apple toolchains by adjusting compiler warning configurations.
  • Improved internal string handling for more reliable inspector protocol communications.

• Performance

  • Optimized message conversion in the debugger inspector, reducing intermediate data structure allocations.