fix: Exclude symbol when checking binding types

[JackRobards]

This PR excludes ES symbol types from unions when checking bindings.
This ensures that nothing and noChange are ignored in type checking.

We remove all symbol types because it is not possible to get the details of symbol types.
This will produce false negatives when other symbols are mixed in, but I consider such situations to be rare.

Closes runem#207. Closes runem#251. Closes runem#316.

This PR does not resolve the issue of ifDefined not supporting null (even though Lit v3 does).
It will probably be resolved when we stop treating ifDefined specially, or when runem#296 is merged.
The user can use either a custom directive or value ?? nothing instead of ifDefined to workaround the issue.

Not a change I made, it is taken from this PR:
runem#364

Thank you to the original author!

I did not include the "node_modules/typescript/lib/lib.es2015.d.ts" addition from the original PR, since I believe it is not needed with the TS updates in this repo 🤞.

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