Implementation of REveText, addition of GL overlay support (prototype).

Contains contributions from Waad, Alja and Matevz. Squashed to avoid adding of
extra files in the repo (some committed by mistake) and to avoid numerous commits.

* Waad: initial implementation & tuning.
* Alja: integration with REve.
* Matevz: final cleanup, loading of fonts & font metrics. Mac and Windows fixes.

Full set of initial development commits is available from:
https://github.com/alja/root/tree/waa-master-2024

Commits to get things working on Mac/Windows and libAfterImage/libpng:
https://github.com/alja/root/tree/waad-revetext-overlay-master-6.33-rb1-final

Related PR in RenderCore: UL-FRI-LGM/RenderCore#20

Demo: tutorials/eve7/texts.C

Update RenderCore version to 1.5.

Location of SDF font and metrics files:

When REveText::AssertSdfFont() is called for the first time it chooses a writable
location in eiter $ROOTSYS/ui5/eve7/sdf-fonts or a ./sdf-fonts in the current
directory.
Alternatively REveText::SetSdfFontDir() can be called beforehand to manually
specify the desired location.

Tag 1st release candidate for v6.32.

[hist] fix similar bug in TSpline5_saveas

Patch release of v6.30 series.

tag: v6-30-04

Tag dev cycle 6.30.03 for next patch release.

Patch release v6.30.02 with an important security fix.

Tag start of dev cycle for upcoming 6.30.02.

Production release ROOT v6.30.00.

Tag begin of development cycle for future v6.32 release.