with #133413 the intent was that VSE Text strips would not use the
fallback font stack if using a custom (non-default) font. However this
determination was done by comparing the font id. This was very weak as
the id can vary quite a bit within the first few fonts. This PR instead
adds a BLF function (BLF_is_builtin) that uses BLF_DEFAULT font flag
instead.
Pull Request: https://projects.blender.org/blender/blender/pulls/135014