Fix-up of: "displayModel.getCaretRect: return a locationHelper.RectLTRB instance", fixes issue in PuTTY

[LeonarddeR]

Link to issue number:

Fixes regressions introduced in #10233

Summary of the issue:

It turns out that when implementing #10233, I used the wrong test case, thereby not actually testing that the changes worked as expected. Therefore, this pr introduces two mistakes:

1. selff instead of self in a method signature
2. Passing ctypes instances to RectLTRB instead of the actual integer values.

Description of how this pull request fixes the issue:

Fixes these issues.

Testing performed:

1. Tested that the caret position is again properly detected and read in putty.
2. Used displayModel.getCaretRect(api.getFocusObject()) in the python console, getting the caret rectangle of the python console input window using the display model.

Known issues with pull request:

None

Change log entry:

None
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