[tui][edi] Loss of caret focus bugs

[nazmulidris]

Cut line

Repro steps:

1. Open an existing MD file (which has more than 1 page in the viewport)
2. Scroll to some place on the 2nd page
3. Delete a line
4. The cursor is gone! You can still type stuff, just don't know where it's landing!

Delete last line

Repro steps:

1. Open an existing MD file (which has more than 1 page in the viewport)
2. Scroll to the last line
3. Delete it
4. The cursor is gone! You can still type stuff, just don't know where it's landing!

Select heading results in wrong caret position

1. Run the examples, Warn on clippy and usage of rust 2018 idoms. #4
2. Place the caret at the start of the editor, then press Shift+End (the heading is selected)
3. The caret is not where its supposed to be it is on the next line
   

In the editor example, opening a dialog and then clearing the contents results in strange UI to be painted on bottom row of dialog

1. Run the examples, Warn on clippy and usage of rust 2018 idoms. #4
2. Press Ctrl+l or Ctrl+k, then select the contents and press delete
3. You will see some strange prompt on the bottom row of the dialog (intentional?)

Wayland support?

Check for wayland support to still work. There were some issues in the rust-scratch/tty repo related to this.