4534: Add call postfix completion r=matklad a=vain0x
To make it easier to wrap an expression with Ok/Some/Rc::new etc.
Note I agree with conclusion of the discussion in #1431 that adding many completions is not the way to go. However, this PR still could be justified due to versatility of use.
Co-authored-by: vain0x <vainzerox@gmail.com>