bug(linux): Key processing with text selection problems (surrounding text)

[ermshiperete]

The test cases for the Text Selection and Key Processing spec show some limitations.

See here for the test cases and the google doc 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⁞