feat(autocmd): add Recording autocmds

feat(eval): add reg_recorded()

This function is used the get the last recorded register.

style(Recording): rename handler to match suggestions

fix(RecordingLeave): send autocommand earlier

This makes the autocommand fire just before setting reg_recorded to
reg_recording, this way we clearly show that we are actually just before
actually quitting the recording mode.

src/nvim/eval.lua

@@ -277,6 +277,7 @@ return {
     readfile={args={1, 3}, base=1},
     reg_executing={},
     reg_recording={},
+    reg_recorded={},
     reltime={args={0, 2}, base=1},
     reltimefloat={args=1, base=1},
     reltimestr={args=1, base=1},