13679: Focus and accessibility improvements of Spin edit controls

[krasko78]

Resolves: #13679

Key points:

1. I changed the accessibility role to SpinBox. My NVDA on Windows now says "Spin button" instead of "Edit".
2. NVDA does read out the new value on change. Since the issue is more than two years old, it will be good to retest it in other screen readers and confirm if they still do not read out the new value.
3. When the value is changed with the arrow buttons or the up/down arrow keys, the spin control will now not lose the focus and will select all the text.
4. If ESC is pressed, the control will lose the focus as before. But if you then try to increase or decrease the value with the up/down arrow keys it won't work. You can however press Space or Enter to focus the control again and change the value further as much as you want.

• I signed the CLA
• The title of the PR describes the problem it addresses
• Each commit's message describes its purpose and effects, and references the issue it resolves
• If changes are extensive, there is a sequence of easily reviewable commits
• The code in the PR follows the coding rules
• There are no unnecessary changes
• The code compiles and runs on my machine, preferably after each commit individually
• I created a unit test or vtest to verify the changes I made (if applicable)

[krasko78]

Only SpinBox was needed here but the enum should be in sync with the one in iaccessible.h (there is comment about that) so I added a few missing values.

[krasko78]

Technically this should be in IncrementalPropertyControl.qml but I figured putting it here shouldn't do any harm. Plus it is much easier to have it here.