RFR: 8282386: JavaFX media stubs rely on libav.org [v2]

[Johan Vos]

> Retrieve libav sources from github.
> Fix JDK-8282386

Johan Vos has updated the pull request incrementally with one additional commit since the last revision:

  Use new naming convention when working with libav files downloaded via github

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Changes:
  - all: https://git.openjdk.org/jfx/pull/989/files
  - new: https://git.openjdk.org/jfx/pull/989/files/600c2f71..b2037246

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=989&range=01
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=989&range=00-01

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jfx/pull/989.diff
  Fetch: git fetch https://git.openjdk.org/jfx pull/989/head:pull/989

PR: https://git.openjdk.org/jfx/pull/989