Lexical: Made a range of selection improvements

Lexical: Made a range of selection improvements

Updated up/down handling to create where a selection candidate does not
exist, to apply to a wider scenario via the selectPrevious/Next methods.

Updated DOM selection change handling to identify single selections
within decorated nodes to select them in full, instead of losing
selection due to partial selection of their contents.

Updated table selection handling so that our colgroups are ignored for
internal selection focus handling.