Simplify play icon shadow

[gaearon]

This solves a few things:

• The shadow was almost invisible on light theme because the shadowColor was theme-dependent (which doesn't make sense when overlaying a video).
• We were getting Raised button causing error: View #... of type RCTView has a shadow set but cannot calculate shadow efficiently which is only solveable by putting a solid background color on the element with the shadow.

Should overall look the same-ish. Here it is against different backgrounds:

[github-actions]

Old size	New size	Diff
8.06 MB	8.06 MB	-263 B (-0.00%)

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[estrattonbailey]

hottt

[mozzius]

I don't exactly get the motivation but it works fine

[gaearon]

I don't exactly get the motivation

See the summary:

• It did not have the same color in dark and light theme, making it essentially invisible with the light theme
  • We do want it to always be visible so that the play button has a bit of contrast against light videos
• We were getting a warning from React Native whenever it rendered ("Raised button causing error: View #... of type RCTView has a shadow set but cannot calculate shadow efficiently") which is probably not good