Bug 459420

SUMMARY
A pet peeve of mine with the default presets is that the pixel art preset doesn't behave the way a user would expect it to on a vanilla Krita installation (tested via flatpak). 

For new pixel artists coming to Krita, especially when working on a 1px scale, ensuring that a pixel is added where intended is an important QOL feature that we should support in this specific preset. I've attached a video illustrating the problem. 

TESTING PROCEDURE
1. Nuke your krita config and start 5.1.1
2. Switch to the pixel art brush. 
3. Go into settings and enable the circle "Brush Cursor Icon" in the "General" tab.
4. Set pixel size to 1 or less. 
5. Try painting on the corners within an intended pixel.


OBSERVED RESULT
There are two noticeable behaviors:
1: `u) Pixel Brush` will not adhere to a 1 pixel grid the way the user would expect for this specific preset when set to 1 pixel. This is because `Sharpness > Align Brush Preview` is disabled by default -- I think it should be on by default on this specific brush.

2: With the default brush preset, on the NW, NE and SW corners the pixels location will seemingly be either off or will similarly be inconsistent with the SE corner. 

EXPECTED RESULT
1: Pixel art brush should conform to pixel grid by default, as that's the intended use-case of this specific brush. 

2: We should try our best to make small brush size stamping as consistent as possible between all 4 corners of a given pixel grid. Perhaps we should even unit-test this specific scenario.

ADDITIONAL INFORMATION
This is low priority, so I've gone ahead and marked it such.