The Table Editor improvements to new line adding (to be Excel-like)

[aik099]

Currently, in table editor mode pressing ENTER at the cursor location in a cell:

• does:
  • (good) add a new line in the current cell
  • (bad) add a new line in other cells of the same row
• doesn't:
  • (bad) split cell content at cursor
  • (bad) preserve contents of other cells

Table before changes:

+------------------------------+-----------+-----------+
| heading 1                    | heading 2 | heading 3 |
+==============================+===========+===========+
| .. config-property::         | line 1    |           |
|    :name: TrimRequiredFields | line 2    | line 2    |
|    :type: int                | line 3    |           |
|                              | line 4    |           |
+------------------------------+-----------+-----------+
| .. config-property::         | line 1    | 200       |
|    :name: MenuFrameWidth     | line 2    |           |
|    :type: int                | line 3    |           |
+------------------------------+-----------+-----------+

Current behavior (pressing ENTER after "line 1" in the middle cell of the 1st row)

+------------------------------+-----------+-----------+
| heading 1                    | heading 2 | heading 3 |
+==============================+===========+===========+
| .. config-property::         | line 1    |           |
|                              |           |           |
|    :name: TrimRequiredFields | line 2    | line 2    |
|    :type: int                | line 3    |           |
|                              | line 4    |           |
+------------------------------+-----------+-----------+
| .. config-property::         | line 1    | 200       |
|    :name: MenuFrameWidth     | line 2    |           |
|    :type: int                | line 3    |           |
+------------------------------+-----------+-----------+

As you can see, the content of the 1st column was affected, but it shouldn't.

Proposed behavior (pressing ENTER after "line 1" in the middle cell of the 1st row)

+------------------------------+-----------+-----------+
| heading 1                    | heading 2 | heading 3 |
+==============================+===========+===========+
| .. config-property::         | line 1    |           |
|    :name: TrimRequiredFields |           |           |
|    :type: int                | line 2    | line 2    |
|                              | line 3    |           |
|                              | line 4    |           |
+------------------------------+-----------+-----------+
| .. config-property::         | line 1    | 200       |
|    :name: MenuFrameWidth     | line 2    |           |
|    :type: int                | line 3    |           |
+------------------------------+-----------+-----------+

Proposed behavior (pressing ENTER inside "line 1" in the middle cell of the 1st row)

+-----------------------------+-----------+-----------+
| heading 1                   | heading 2 | heading 3 |
+=============================+===========+===========+
| .. config-property::        | li        |           |
|    :name: TrimRequiredFields| ne 1      |           |
|    :type: int               | line 2    | line 2    |
|                             | line 3    |           |
|                             | line 4    |           |
+-----------------------------+-----------+-----------+
| .. config-property::        | line 1    | 200       |
|    :name: MenuFrameWidth    | line 2    |           |
|    :type: int               | line 3    |           |
+-----------------------------+-----------+-----------+