Expose all sws flags for `frame.reformat(interpolation=...)`

[oakaigh]

Currently pyav only exposes a limited number of flags (AND as enum.IntEnums RATHER THAN enum.IntFlags; so that needs to change as well - otherwise Interpolation is not useful):

PyAV/av/video/reformatter.py

Lines 10 to 21 in baebfed

	class Interpolation(IntEnum):
	FAST_BILINEAR: "Fast bilinear" = SWS_FAST_BILINEAR
	BILINEAR: "Bilinear" = SWS_BILINEAR
	BICUBIC: "2-tap cubic B-spline" = SWS_BICUBIC
	X: "Experimental" = SWS_X
	POINT: "Nearest neighbor / point" = SWS_POINT
	AREA: "Area averaging" = SWS_AREA
	BICUBLIN: "Bicubic luma / Bilinear chroma" = SWS_BICUBLIN
	GAUSS: "Gaussian approximation" = SWS_GAUSS
	SINC: "Unwindowed Sinc" = SWS_SINC
	LANCZOS: "3-tap sinc/sinc" = SWS_LANCZOS
	SPLINE: "Unwindowed natural cubic spline" = SWS_SPLINE

And other flags available (such as full_chroma_int, bitexact, accurate_rnd) are not exposed:
https://github.com/FFmpeg/FFmpeg/blob/44d082edc87381d978e8588b148116b99fefdb43/libswscale/options.c#L34-L54

Related discussion:
#1617