webShareDialog: Use JS String.startsWith()
webShareDialog: Use JS String.startsWith()

It's faster to use JS string methods than to trampoline into C.
Miscellaneous cleanup.

https://phabricator.endlessm.com/T21017

endlessm/eos-knowledge-lib,endlessm/eos-knowledge-lib,endlessm/eos-knowledge-lib,endlessm/eos-knowledge-lib