refactor(vim): make priority ordering of LSP selection obvious
refactor(vim): make priority ordering of LSP selection obvious

Use `if`/`elseif`/`else` to make clear that we want to use
typescript-language-server if available first, and only use
javascript-typescript-langserver as a fallback.

My old "system", of just commenting out one or the other, wasn't very
intention-revealing at all.

wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent