Add SkEncodedInfo to report properties of encoded image data

Add SkEncodedInfo to report properties of encoded image data

All this does is build an SkEncodedInfo for each codec, and
then convert it to an SkImageInfo.

In future steps I intend to:
(1) Use SkEncodedInfo in place of SrcConfig in SkSwizzler.
(2) Support more conversions in SkSwizzler (non-native
BGRA/RGBA, 16-bit components, float, fixed point)
(3) Investigate optimizing conversions from encoded data
to linear color spaces.

BUG=skia:4133
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1820073002

Review URL: https://codereview.chromium.org/1820073002