Replace imported SDK_INT constants with actual numbers

[consp1racy]

Some of my favorite candidates for fix are in RealBitmapPool:

if (SDK_INT >= O) {
    configs += Bitmap.Config.RGBA_F16
}

require(SDK_INT < O || config != Bitmap.Config.HARDWARE) { "Cannot create a mutable hardware Bitmap." }

Using actual API level values will promote readability, i.e. nobody will have to ponder for minutes why the hell do we check whether SDK_INT is less than, greater than or equal to zero.

See https://twitter.com/jakewharton/status/1049421501559128065 for discussion. Main points:

• [JWh] Just use the numbers. They already convey what you want. @RequiresApi(21), minSdkVersion 21, setWhateverApiLevel(21). CAN_USE_THING_API_LEVEL = 21.
• [JWa] Agree, though this doesn't solve the practical issue of being unable to find API-specific code reliably. Searching for two digits in a large project is still painful. Searching for @RequiresApi, @SdkSuppress, Build.VERSION.SDK_INT, and comments is less painful but not obvious.
• [JWh] True! Although I rarely need to find all of those at once. Usually it's just one and you always need to use the annotation/field because someone may have used a number or a semantic constant like FINGERPRINT_ENABLED.

[mario]

@colinrtwhite taking this over.

[colinrtwhite]

@mario Thanks, but I'd hold off for the moment (still debating if we should make this change). I generally agree that using numbers is more consistent, however Build.VERSION_CODES seems like the standard.

[mario]

@colinrtwhite sounds good.