With non-TeX fonts, you can select a 'Non-TeX Font Default' math font, which simply loads unicode-math without actually selecting a math font, this then uses the default math otf font, currently Latin Modern. Other fonts still need to be set manually in the preamble, via \setmathfont.
The implementation suppresses unneeded package requests from unicodesymbols, but the output still uses macros instead of full unicode (both is possible with unicode-math).
The whole thing is a proof of concept, and it needs to be tested. I have tested it with the math manual, which compiles and seems to display correctly if I remove some hardcoded package loadings. OTOH I have not much experience with math.
This addresses #7449 partly.
\IfFileExists does not search in texmf/fonts, so the \TestPackage test fails for font files. Add a new \TestFont check that adapts the font check from ltxcheck.tex.
This is needed for the minion2newtxmath test, since this package only consists of font files,
In 0aead96461 it was introduced that the toolbar popup menu buttons are not
initialized until they are being used (i.e. pressed at for the first
time). As a consequence, these buttons are always enabled on start. Now
that we have the sticky button for view and update, I'm now annoyed by
this every time I start LyX.
This addresses #6543 by adding an option to prevent fonts such as Palatino and Times to automatically adapt the math font (IOW it lets you load the text font only for a bunch of fonts where this is easily possible).
Furthermore it adds an interface to select a specific math font, which is defined in latexfonts. Currently, this is only euler (the only one I know), but if there are other math-only tex fonts, they can be added easily (but note that this changes the file format).
Non-TeX math fonts are not yet supported. Eventually, unicode-math support can use the existing UI, but this is not on my agenda.
The LaTeX font now do not specify simply alternative packages or packages for OT1 encoding etc., but they refer to complete AltFonts (which are not directly accessible via the GUI). This way, alternative fonts can also have options (osf, sc etc.), and they can use all sorts of initializing methods (\usepackage, \setrmfamily etc.).
