Fixes #1922373. Resolves a case of keys collision in Resources' cache.

The Resources class keeps a cache of known resources. The keys used by the
cache are stored as int primitives. For any given drawable resource, a key
is built thusly:

TypeValue.assetCookie << 24 | TypedValue.data

In the case of a plain color drawable, assetCookie always equals -1, that
is 0xFF once right-shifted and the data contains the color value. Which
means the key for the following two colors is the same:

0xFF000000
0x00000000

Because of the int storage and the use of the (constant in this case)
asset cookie, the alpha channel of a color is ignored. That means that
if you first load an opaque black color (0xFF000000), subsequent loads
of a totally transparent black color (0x00000000) will give you an
opaque black color.

A workaround is to use a transparent color that is not black,
0x00000001 for instance. Note that this issue would arise with any color
and any opacity level.

The solution to fix this issue is simply to change the cache to use
longs instead of ints to represent the keys. A key thus becomes:

TypedValue.assetCookie << 32 | TypedValue.data

This allows us correct storage of all colors at the cost of a few bytes.
The tradeoff is that we can keep caching ColorDrawable, which is
definitely worth it.