Watch mode errors on scope changes after transpilation

There's an issue with watch mode where field initialisers will trigger diagnostic errors after their scope is transpiled. This only happens after the app has already been transpiled.

Here's a unit test that shows the issue:

it('does not pollute the AST after validation', () => {
    const file = program.setFile<BrsFile>('source/lib.bs', `
        class HasPropertyInitialiser
            name as string = createObject("roString")
            sub new()
                super()
            end sub
        end class
    `);
    program.validate();
    file.transpile();
    program.setFile<BrsFile>('source/another.bs', `
        class AnotherClassJustToInvalidateScope
        end class
    `);
    program.validate();
    expectZeroDiagnostics(program.getDiagnostics());
});

Start with the supplied unit-test sequence using program.validate(), file.transpile(), program.setFile(), and program.getDiagnostics(). Reproduce the diagnostic errors after transpilation, then trace how validation and scope invalidation interact with the transpiled AST. Done means the test produces zero diagnostics after the second validation.