Fixes #13935

Reasoning behind implementation chosen:

• a.b.c prefix in a.b.c.<tab> needs to be preserved as otherwise the completer will replace it with completion rather than appending (so we cannot just use .suffix, we need to use a.b.c.suffix here)
• as in the issue we cannot use a b.suffix but need to use b.suffix or .suffix
• d['a b'] prefix cannot be split using space splitting so we need to tokenize
• however, we can do either a[0].suffix or .suffix