message_edit: Refactor handle_edit_keydown to separate inline topic edits.
message_edit: Refactor handle_edit_keydown to separate inline topic edits.

This commit cleans up the dirty if/else structure of
handle_edit_keydown by switching to switch case statements, and also
separates the handler for inline_topic_edits and that for message
row edits.

eeshangarg/zulip,synicalsyntax/zulip,eeshangarg/zulip,zulip/zulip,timabbott/zulip,punchagan/zulip,andersk/zulip,showell/zulip,zulip/zulip,kou/zulip,andersk/zulip,showell/zulip,showell/zulip,timabbott/zulip,synicalsyntax/zulip,synicalsyntax/zulip,punchagan/zulip,punchagan/zulip,andersk/zulip,eeshangarg/zulip,synicalsyntax/zulip,zulip/zulip,timabbott/zulip,zulip/zulip,shubhamdhama/zulip,hackerkid/zulip,shubhamdhama/zulip,brainwane/zulip,zulip/zulip,hackerkid/zulip,kou/zulip,eeshangarg/zulip,rht/zulip,andersk/zulip,kou/zulip,punchagan/zulip,hackerkid/zulip,rht/zulip,kou/zulip,rht/zulip,synicalsyntax/zulip,synicalsyntax/zulip,rht/zulip,hackerkid/zulip,punchagan/zulip,brainwane/zulip,brainwane/zulip,zulip/zulip,showell/zulip,eeshangarg/zulip,shubhamdhama/zulip,shubhamdhama/zulip,brainwane/zulip,hackerkid/zulip,timabbott/zulip,kou/zulip,rht/zulip,kou/zulip,timabbott/zulip,zulip/zulip,andersk/zulip,eeshangarg/zulip,kou/zulip,shubhamdhama/zulip,brainwane/zulip,punchagan/zulip,showell/zulip,shubhamdhama/zulip,synicalsyntax/zulip,rht/zulip,andersk/zulip,timabbott/zulip,hackerkid/zulip,showell/zulip,brainwane/zulip,showell/zulip,eeshangarg/zulip,timabbott/zulip,hackerkid/zulip,andersk/zulip,punchagan/zulip,brainwane/zulip,rht/zulip,shubhamdhama/zulip