Media: Reduce failing uploads following 4.7.1.

[39831] introduced more strict MIME type checking for uploads, which
resulted in unintetionally blocking several filetypes that were
previously valid. This change uses  a more targeted approach to MIME
validation to restore previous behavior for most types.

Props blobfolio, iandunn, ipstenu, markoheijnen, xknown, joemcgill.
Fixes #39550, #39552.

git-svn-id: https://develop.svn.wordpress.org/trunk@40124 602fd350-edb4-49c9-b593-d223f7449a82

tests/phpunit/data/uploads/video-play.svg

@@ -0,0 +1,5 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<svg xmlns="http://www.w3.org/2000/svg" version="1.1" width="64" height="64">
+	<circle cx="32" cy="32" r="25" stroke="white" stroke-width="7" fill="black" fill-opacity="0.2"/>
+	<polygon points="26,22 26,42 43,32" fill="white"/>
+</svg>