Secondary color support in the paint editors, and associated
operators:
* X key swaps secondary and primary colour
* Ctrl-lclick painting uses the secondary colour
* Shift-S samples colour for the secondary colour

This can obviously be used for background/foreground palettes it will
obviously be used for gradient effects later on.

merge with trunk version 57545

Attempt to fix #35548:

Use nearest edge instead of nearest vertex for UV island selection, or
you may get a far away UV island that happens to have a vertex nearby.

Fix #35774 Confusing Text in Texture Paint Panel

A simple copy-paste error.

Fix compilation of cycles for MinGW-w64 after recent commits. MinGW-w64 has conflicting redefinitions of the SSE functions in windows.h, so we will be using this header instead, since we can't always avoid including it instead of the sse headers.

OpenExr version 2.0.0 for MinGW-w64. Also recompiled OpenImageIO to reuse the same library.

Fix #35651, #35645.
Hidden faces do not get UvElements generated so essentially this caused
a null point reference on edge lookup.

Obsessive Null Checking Compulsion case:
Textured draw mode + DynTopo crashed after recent specularity tweak.

Commit static version of zlib 1.2.6 (same as the one used in mingw64)

Fix compilation on MinGW32 scons. The compiled library there is already static, revert renaming of linked library