Improve code action invocation with no selection

When we don't have a selection, prefer word range over the current
position instead of the full line range which doesn't result in anything
useful with at least two servers: clangd and dart-analyzer.

clangd can provide code action for example if the word under cursor
is a macro or 'auto'.

dart-analyzer similarly provides useful actions for word under cursor.

(cherry picked from commit 1e276c53)