Switch expression causes crash when merging multiple cases

[kenzieschmoll]

Original discussion on this PR: flutter/devtools#5671

Even though the analyzer does not report any errors, this code does not build:

    final SourceLocation? sourceLocation = switch (object) {
      FieldRef(:final location) ||
      FuncRef(:final location) ||
      ClassRef(:final location) =>
        location,
      _ => null,
    };

FieldRef.location, FuncRef.location, and ClassRef.location all have a type of SourceLocation?, but the following build error occurs:

lib/src/screens/debugger/program_explorer_model.dart:349:23: Error: Variable pattern 'location' doesn't have the same type or finality in all cases.
      FieldRef(:final location) ||
                      ^^^^^^^^

CC @scheglov