[vm] support redirecting external const factory constructors

[dcharkes]

[...]
dart.ffi.Array.Array

stderr:
Unimplemented handling of missing static target

--- Re-run this test:
python tools/test.py -n dartk-linux-release-x64 lib_2/mirrors/invocation_fuzz_test/none

Happens when using patch file to implement an external const factory as a redirecting factory constructor.

class Array<T extends NativeType> extends NativeType {
  external const factory Array(int dimension1);
}

patch file:

@patch
@pragma("vm:entry-point")
class Array<T extends NativeType> {
  // ...

  @patch
  const factory Array(int dimension1) = _ArraySize<T>;
}

class _ArraySize<T extends NativeType> implements Array<T> {
  final int dimension1;

  const _ArraySize(this.dimension1);
}

Does not happen without using patch files:

class Array<T extends NativeType> extends NativeType {
  const factory Array(int dimension1) = _ArraySize<T>;
}

class _ArraySize<T extends NativeType> implements Array<T> {
  final int dimension1;

  const _ArraySize(this.dimension1);
}

[dcharkes]

The workaround in mentioned CL should be undone before next stable release.

[dcharkes]

In debug mode

../../runtime/vm/compiler/frontend/kernel_translation_helper.cc: 436: error: expected: IsProcedure(procedure)

IsConstructor(procedure)
true
IsProcedure(procedure)
false

@#C17
    @#C17
    static factory /* from org-dartlang-sdk:///sdk/lib/_internal/vm/lib/ffi_patch.dart */ •<T extends ffi::NativeType = ffi::NativeType>(core::int dimension1) → ffi::Array<ffi::Array::•::T>
      let dynamic #redirecting_factory = ffi::_ArraySize::• in let ffi::Array::•::T #typeArg0 = null in invalid-expression;

dart::Assert::Fail(dart::Assert * this, const char * format) (/usr/local/google/home/dacoharkes/master/sdk/runtime/platform/assert.cc:44)
dart::kernel::TranslationHelper::DartProcedureName(dart::kernel::TranslationHelper * this, dart::kernel::NameIndex procedure) (/usr/local/google/home/dacoharkes/master/sdk/runtime/vm/compiler/frontend/kernel_translation_helper.cc:436)
dart::kernel::TranslationHelper::LookupStaticMethodByKernelProcedure(dart::kernel::TranslationHelper * this, dart::kernel::NameIndex procedure) (/usr/local/google/home/dacoharkes/master/sdk/runtime/vm/compiler/frontend/kernel_translation_helper.cc:610)
dart::kernel::StreamingFlowGraphBuilder::BuildStaticGet(dart::kernel::StreamingFlowGraphBuilder * this, dart::TokenPosition * p) 

The target of a static get can be a Constructor, which is not supported by the VM currently.

N.b. The StaticGet an encoding of the redirection, there's no executable semantics.

Thanks @stefantsov for the background knowledge!

[dcharkes]

Related issues #28421 and #28424.

Turns out the VM was trying to compile the invalid expressions because of a missing flag (which was not visible in the textual representation of kernel): 2 line fix. Combining that fix with parsing an additional tag in the VM might work.