deperecate FlxMath.fastSin and FlxMath.fastCos

[Vortex2Oblivion]

as pointed out here in #3215
fastSin and fastCos are just lies and straight up slower in most cases (except for hashlink it seems)

[DetectiveBaldi]

Some notes:
fastCos is seemingly faster on JavaScript and HL, fastSin is faster only on HL (both are slower on eval, and the supplied sample timeouts on neko)
I think there is some value to just adding a couple of compiler conditions instead of deprecating, but at the same time, there are very few situations in which a dev will need to use cos and sin so many times that the (target dependent) speed increase will become noticeable

[Vortex2Oblivion]

from my testing its slower on every target but hl java and php

[Geokureli]

I'm not really interested in maintaining a fast math library in haxe. If people want a slightly faster sin/cos at some cost in accuracy they should look at math haxelibs. I did a quick search and couldn't find any fast trig/math haxelibs, indicating there isn't enough demand for this to justify maintaining one

Also, as I stated in #3215 (which, in retrospect seems more rude than I intended, sorry): I want people to submit PRs that fix issues they are personally facing, or result in meaningful improvements to their own project. Not features for hypothetical devs

[Vortex2Oblivion]

Yeah that makes sense I just thought it was strange there was sine and cosine but not tangent
then i found out that the functions are a lie and slower than the standard library lol

[Geokureli]

Yeah that makes sense I just thought it was strange there was sine and cosine but not tangent then i found out that the functions are a lie and slower than the standard library lol

No, I know, I was responding to Baldi's message

I think there is some value to just adding a couple of compiler conditions instead of deprecating

Plus there's a 85% chance that the accuracy of fastSin is off by more than 0.0001 which is significant, imo