Support foreign namespace behaviour in language-server and svelte2tsx

[halfnelson]

This allows for case sensitive attributes in the JSX via the foreign namespace. Which then allows svelte-nodegui and svelte-native to use the correct casing of attribute names and avoid errors at runtime.

This involved wiring through the svelte compiler config from the language server into svelte2tsx then into htmlxtojsx

Bonus feature, I can run yarn test on windows due to cross-env