Bind Fts5ExtensionApi::xUserData() to JNI and extend xCreateFunction() to accept...

Bind Fts5ExtensionApi::xUserData() to JNI and extend xCreateFunction() to accept that argument. In test code, use assert() instead of exceptions if assert() is enabled so that test failures (exceptions) thrown via callbacks do not get suppressed (which they otherwise necessarily are to avoid crashing the host app).

FossilOrigin-Name: e43837377696e468cd31cf71585fe235ffe67a9f4d3b036c5f9d0cb7141d0f57