@sandersn said he wanted to do this while updating our jsdoc parser, but kept running into infinite loops in the parser. With the general fix to that issue applied in #17420, isStartOfParameter can now be less ad-hoc and express its intent better, by using isStartOfType in full.

This changes our parser errors (and thereby our emit) on a pair of bad-parse baselines, arguably for the better (since the kinda-parameter lists actually get parsed as such now, rather than as parenthesized expressions).