Merge mesa-dri and mesa-libs, upgrade to 19.2.8

[voidanix_420blaze.it]

Summary

Keeping them split seems (to me, at least) unnecessary and confusing since patches that need to track mesa upgrades have to touch both ports

This is still work in progress and definetly not production quality

Test Plan

This still needs to be tested as most big ports rely on mesa-libs and I only have an amdgpu to test this on

[val_packett.cool]

https://github.com/myfreeweb/freebsd-ports-dank/blob/lite/graphics/mesa-dev/Makefile

[voidanix_420blaze.it]

In D23161#507739, @greg_unrelenting.technology wrote:

https://github.com/myfreeweb/freebsd-ports-dank/blob/lite/graphics/mesa-dev/Makefile

oof I should learn how to use the internet.
Wondering if it's OK to abandon this since you already got further than I did

[voidanix_420blaze.it]

Bump PORTREVISIONs, use less problematic patches, bump python to 3.6+