Several IME fixes

[lxatstariongroup]

Prerequisites

• [x] I have written a descriptive pull-request title
• [x] I have verified that there are no overlapping pull-requests open
• [x] I have verified that I am following the COMET-IME code style guidelines
• [x] I have provided test coverage for my change (where applicable)

Description

466

958

1202

1203

1338

[lxatstariongroup]

@samatstariongroup @antoineatstariongroup Please review per commit. Every commit is a separate issue.