FED-1881 Fix regression in SyntheticEvent mock class type-checking

[greglittlefield-wf]

Motivation

When testing these changes, we ran into a case where a consumer was mocking type, and relying on type-checking utilities to respect that.

class MockSyntheticEvent extends Mock implements SyntheticEvent {}

final mockEvent = MockSyntheticEvent();
when(mockEvent.type).then('click');
print(mockEvent.isMouseEvent);

Previously, this would print true, but in v7_wip, it prints false.

Solution

• Update event type checking to match old behavior.
• Add regression test and additional test

Testing

• Verify that regression test fails in the commit before the fix was introduced
  • CI link: https://github.com/Workiva/react-dart/actions/runs/6817966382/job/18542598172
  • Expected failing test: Synthetic event helpers SyntheticEventTypeHelpers checks types correctly for Mock objects withtypemocked
• Verify that regression test pass after the fix was introduced (latest CI passes)

[aviary2-wf]

Security Insights

No security relevant content was detected by automated scans.

Action Items

• Review PR for security impact; comment "security review required" if needed or unsure

• Verify aviary.yaml coverage of security relevant code

  Questions or Comments? Reach out on Slack: #support-infosec.

[robbecker-wf]

QA+1 CI passes with updated/new tests that cover the functionality

[greglittlefield-wf]

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