Format unique symmbol string output with unique symbol and not typeof within checker

[weswigham]

A tests was added between when #21403 was opened and merged that is affected by it (and is now breaking our build). The output seems fine.

[sandersn]

I don't know, it looks wrong, but I'd merge this and investigate why the code changed the baseline afterward.

[sandersn]

Specifically, it's strange that in const x: string = Symbol(), the error is that 'typeof x' isn't assignable to 'string', since 'typeof x' is string — it's x's initializer that's not assignable to string.

[weswigham]

@sandersn Changed typeToString to internally use unique symbol by default, since it's preferable there.