hg: openjfx/11-dev/rt: 8218174: Add missing license file for Mesa header files

[johan at lodgon.com]

Changeset: 6d9e3d56bf85
Author:    kcr
Date:      2019-02-19 13:22 -0800
URL:       https://hg.openjdk.java.net/openjfx/11-dev/rt/rev/6d9e3d56bf85

8218174: Add missing license file for Mesa header files
Reviewed-by: prr

+ modules/javafx.graphics/src/main/legal/mesa3d.md