Inverted tab-suggestions for argument values in entity selectors are suggested even if the typed prefix doesn't include an exclamation mark

Affects 18w09a

Affects 18w10d

Copy-pasta from MC-124990:

Part of this bug fix should be a change to how inversion (and by extension tags etc.) is handled by the suggestion engine.

Currently, every possible inversion is listed in the suggestion list.  Instead, aside from the list of suggestions, a single suggestion at the top, ! (or in the case of tags, #) should be included.  Then, after (if) the ! (or #) is entered, the suggestion list should again appear, rather than the current behavior which attempts to parse the ! as the entire value, and generates an error which suppresses the list of suggestions.