Deprecate FlxPoint.angleBetween and make angles consistent

[Geokureli]

fixes #2037 and #956

Created FlxAngle.angleFromOrigin, and changed every "angle from coordinates" util to use it, just about everywhere and made 0 degrees point RIGHT everywhere. 2037 hit a road block looking for a "fast atan", but I hardly think it's worth the extreme lack of precision

I ran some speed tests, here:

// --- HashLink ---
// label  [times run]          total time         adjusted time
slow check  [1000000] - 11.4790916442871   - 3.87918949127197
fast check  [1000000] - 8.74979496002197   - 1.14989280700684
return 1.0  [1000000] - 7.59990215301514   - 0
// --- JS ---
slow check [10000000] - 5.874000000059604  - 3.6850000001490115
fast check [10000000] - 4.197000000029803  - 2.00800000011921
return 1.0 [10000000] - 2.188999999910593  - 0
// --- Neko ---
slow check   [100000] - 10.0919961929321   - 1.1138916015625
fast check   [100000] - 16.0075902938843   - 7.02948570251465
return 1.0   [100000] - 8.97810459136963   - 0

is it faster? Ignoring neko, it's roughly 2-3 times faster when adjusted against a simple literal return! however, these gains will likely never have a significant impact, and if someone needs that optimization (and less precision), they probably know how to make their own. Even if we could fix the lack of precision, this speed bonus just seems frivolous. However if we do want to replace Math.atan2 with something else, we can now change one spot to affect everything in the framework.

Note: FlxSwipe and FlxPath angles no longer have their previous 90 degree offset. this should be the only backwards compatibility issue this PR introduces

Additional changes

• Added FlxAngle utlis: degreesBetween, radiansBetween, degreesBetweenPoint, radiansBetweenPoint, degreesBetweenMouse, radiansBetweenMouse, degreesBetweenTouch and radiansBetweenTouch
• Deprecated FlxAngle utils: getCartesianCoords, getPolarCoords and angleFromFacing
• Added degrees and radians fields to FlxDirectionFlags to replace FlxAngle.angleFromFacing