Bumping the minimum version of macOS on which JavaFX will run to 10.12

[Kevin Rushforth]

The proposed fix for JDK-8265031 [1], which is under review as PR #462 
[2], will bump the minimum version of macOS on which JavaFX will run to 
10.12 (for x86_64 systems) to match the minimum version that the JDK 
will run on. After this fix is integrated, builds of JavaFX will no 
longer run on macOS 10.10 or 10.11. I don't imagine anyone is still 
running anything that old, but wanted to make sure the impact of this 
was understood.

This also bumps the minimum version for aarch64 systems to 11.0, which 
also matches the JDK. Since Apple only added support for aarch64 in 
macOS 11, this will have no impact.

-- Kevin

[1] https://bugs.openjdk.java.net/browse/JDK-8265031
[2] https://git.openjdk.java.net/jfx/pull/462