Add Dart 3.13 single-snapshot support

[Techuouo520]

Summary

Dart 3.13.0-282.3.beta removed the VM isolate and switched AOT snapshots to a single-snapshot layout. Blutter still assumed the old VM + isolate snapshot model, so apps built with this Dart version could not be loaded.

This PR adds support for the new layout while keeping the existing code path for older Dart versions. Dart 3.13-specific behavior is guarded by BLUTTER_DART_SINGLE_SNAPSHOT.

What changed

Dart 3.13 changed a few VM internals that Blutter relied on:

• The four _kDartVm* / _kDartIsolate* snapshot symbols were replaced by _kDartSnapshotData and _kDartSnapshotText.
• Dart_InitializeParams no longer accepts a VM snapshot.
• OBJECT_STORE_STUB_CODE_LIST was removed and the relevant stubs moved into VM_STUB_CODE_LIST.
• ObjectStore::throw_stub() and StubCode::HasBeenInitialized() are gone.
• Closure context and delayed type arguments no longer have fixed offsets and now live in the variable-length elements[] area.
• Some type-context entries can be null, where null effectively means dynamic.

There were also a few Windows build issues exposed by the newer Dart sources: __VA_OPT__ requires /Zc:preprocessor, UTF-8 source files need /utf-8 on non-UTF-8 Windows codepages, and Dart 3.13's regexp code now requires the matching ICU 73 libraries instead of the Windows SDK ICU.

Implementation

The main changes are:

• extract_dart_info.py / ElfHelper.cpp
  • support the new two-symbol snapshot layout
  • keep the old symbol lookup as a fallback
• DartLoader.cpp
  • initialize Dart without a separate VM snapshot on Dart 3.13
  • treat Dart 3.13 snapshots as strong null safety
• DartStub.h / DartApp.cpp
  • build and load stubs from VM_STUB_CODE_LIST for the new VM layout
• DartTypes.cpp
  • treat null type slots as Type::DynamicType()
  • include the CID and class name in invalid-type errors to make failures easier to diagnose
• CodeAnalyzer_arm64.cpp / FridaWriter.cpp
  • temporarily skip the old fixed-offset closure context / delayed-type-argument analysis
  • TODOs are left in place for reimplementing this against elements[]
• Windows build
  • add /Zc:preprocessor
  • add /utf-8
  • link against the bundled/matching ICU 73 libraries

Validation

Tested end-to-end with an ARM64 libapp.so built using Dart 3.13.0-282.3.beta. Blutter successfully produces:

• asm/
• pp.txt
• objs.txt
• blutter_frida.js
• ida_script/

There is still one non-fatal handleOptionalNamedParameters INSN_ASSERT during analysis, but it does not stop output generation.

Known limitation

Closure parameter and generic-type inference is currently less complete on Dart 3.13 because the old analysis depended on fixed closure offsets. Supporting the new elements[] layout properly should be handled separately.

Older Dart versions continue using the existing code paths unchanged.