Navigation Control Border Re-Implementation

[ArjunBoi]

Resolves: #8442

All elements supporting Navigation Control now draw the border rectangle on the outside.
There were a total of 5 different elements i.e.

• Dropdown: (it works for the main Dropdown item, but the items inside it are very close together. I have implemented this in such a way that the borders for the popup elements are drawn on the inside).
• DockPanelTab : The borders are being drawn on the inside, again because of lack of space.
• InstrumentsTreeItemDelegate : Borders on the inside, same reason.
• PaletteTree : This file uses ListItemBlank as a delegate to draw its children. I've done it in such a way such that only this instance of ListItemBlank 's borders get drawn on the inside.
• Expandable Blank : Same thing

The borders for these are drawn on the inside, in a way that it does not interfere with the High-Contrast borders; i.e. the HC 1px border + the 2px navCtrl border will combine to make a single 3px border on the inside (the innermost being the HC border, followed by the navCtrl one).

For a demonstration, Navigate to DevTools -> KeyNav. (Please make sure that you are in Light mode. The colors for the elements in that page are hard-coded and don't work well with other themes)

This PR does not modify the existing Navigation Control logic for elements, just the way the borders are drawn around them.

• I signed CLA
• I made sure the code in the PR follows the coding rules
• I made sure the code compiles on my machine
• I made sure there are no unnecessary changes in the code
• I made sure the title of the PR reflects the core meaning of the issue you are solving
• I made sure the commit message(s) contain a description and answer the question "Why do those changes fix that particular issue?" or "Why are those changes really necessary as improvements?"
• I made sure the commit message title starts with "fix #424242:" if there is a related issue
• I created the test (mtest, vtest, script test) to verify the changes I made

[ArjunBoi]

There are a lot of bugs within the Navigation Control system that made testing very troublesome.
There were elements that were mentioned only in a few places in the code, which were out of the reach of NavigationControl and thus weren't test-able immediately.

In other places, the application would often crash trying out the different options. I also encountered behavior in which i would press space to select an option in a group of FlatRadioButtons, and the application wouldn't update the changes made because of having that button selected. The changes were only made once i clicked that button with my mouse. In the same element, pressing "Enter" instead of "Spacebar" led to a crash. (I found this behavior in the Text settings in the Inspector/Properties tab)