[ai-completion] LLM-11886: make AI completion invoke on Enter when IdeaVim is turned on

[kkarnauk]

Before, the Inline Completion providers (like Full Line Code Completion and AI Assistant Completion) weren't triggered by an Enter hit. It fixes the problem.

Please note that inline.completion.enter handler will be available since the tomorrow build. But it looks like it doesn't create problems for the previous versions of IDE (the missing action handler).