Improvements to function completion with namespaces

[albertoventurini]

Function name completion with namespaces doesn't work well. I suspect namespaces are erroneously parsed as PropertyLookups (to be verified). After a dot, the completion provider starts afresh with a new list of suggestions, which don't account for the namespace part that is already typed.

Without namespaces, function completion works as expected:

When a dot is typed, function completion starts afresh:

Result: a part of the namespace is inserted twice: