bug(developer): Key processing with text selection problems

The test cases for the [Text Selection and Key Processing spec](https://github.com/keymanapp/keyman/issues/9073) shows some limitations in Keyman Developer (Debugger Mode).

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.

## Failed tests:

1. (T04) `^⁞X⁞` in doc. Typing `A`.
Expected result: `Â⁞`
Actual result: `^A⁞`
2. (T05) `^⁞X the quick brown fox⁞` in doc. Typing `A`.
Expected result: `Â⁞`
Actual result: `^A⁞`
3. (T15) Type `X`, `a` followed by `[K_BKQUOTE]` and `b`. Select `b` (`Xa⁞b⁞`).
Press `BKSP` twice.
Expected result: `X`
Actual result: `Xfail2`
4. (T16) Type `X`, `a` followed by `[K_BKQUOTE]` and `b`. Select `b` (`Xa⁞b⁞`).
Press `BKSP` then `o`.
Expected result: `Xao`
Actual result: `Xaok3`