bug(linux): Key processing with text selection problems (compliant apps)

The test cases for the [Text Selection and Key Processing spec](https://github.com/keymanapp/keyman/issues/9073) show some limitations.

See [here](https://github.com/keymanapp/keyman/issues/9073#issuecomment-1801356344) for the test cases and the [google doc](https://docs.google.com/spreadsheets/d/1NDO82y77C45pw_ZcMPcD36NZ4VUy9hQcuByieyeJVtM/edit?usp=sharing) for the test results.

Keyman 17.0.208
Ubuntu 22.04.3 LTS
ibus 1.5.28-3sil2~jammy
gedit 41.0

## Failed tests:

1. (T01) : `^⁞X the quick brown fox⁞A` in doc. Typing `BKSP`.
Expected result: `^⁞A`
Actual result: `foo⁞A` or `^foo⁞A` (depending on direction of selection)
2. (T02) `^⁞X the quick brown fox⁞` in doc. Typing `BKSP`, then `A`.
Expected result: `Â⁞`
Actual result: `foo⁞A` or `^foo⁞A` (depending on direction of selection)
3. (T03) `⁞^⁞` in doc, selection as indicated, typing `A`.
Expected result: `A⁞`
Actual result: `Â⁞`
4. (T06) `^⁞X⁞` in doc. Typing `BKSP`.
Expected result: `^⁞`
Actual result: `foo⁞` or `^foo⁞` (depending on direction of selection)
5. (T07) `^⁞X⁞` in doc. Typing `BKSP`, `BKSP`.
Expected result: `foo⁞`
Actual result: `fo⁞` or `^fo⁞` (depending on direction of selection)
6. (T09) `a⁞bc de⁞` in doc with selection starting at `b`. Typing `BKSP`.
Expected result: `a⁞`
Actual result: `a⁞bc d⁞`
7. (T10) `a⁞bc de⁞` in doc with selection starting at `e`. Typing `BKSP`.
Expected result: `a⁞`
Actual result: `⁞bc de⁞`
8. (T11) `abc ⁞de⁞ fg` in doc. Typing `BKSP`.
Expected result: `abc ⁞ fg`
Actual result: `abc ⁞d⁞ fg`
9. (T13) `abc⁞` in doc. Typing `BKSP`.
Expected result: `ab⁞`
Actual result: `ab⁞c⁞`
10. (T15) Type `X`, `a` followed by `[K_BKQUOTE]` and `b`. Select `b` (`Xa⁞b⁞`).
Press `BKSP` twice.
Expected result: `X⁞`
Actual result: `⁞b⁞`
11. (T16) Type `X`, `a` followed by `[K_BKQUOTE]` and `b`. Select `b` (`Xa⁞b⁞`).
Press `BKSP` then `o`.
Expected result: `Xao⁞`
Actual result: `Xo⁞`