Continue to support specififying logical font sizes in the compile step
via SLINT_FONT_SIZES, but additionally look for Text/TextInput/Window elements
and extract any constant font sizes
found.
This makes it work out of the box with the printer demo.
The code was mixing logical and physical sizes, causing glyphs being
doubly scaled down. Instead, this patch introduces:
* Physical* and Logical* euclid length/size/rect aliases
* some extraction traits for getting the scalars in rects/sizes as lengths (until euclid has them
built-in)
* wrapper traits/types for safely extracting the physical font metrics the
compiler generates (i16)
* Fix a bug in the text height calculation where we failed to take the
descent into account
Enable with `SLINT_EMBED_GLYPHS=1` and select sizes like
`SLINT_FONT_SIZES=12,16`
This change just puts the data structures in place, rasterizes a fixed
subset, embeds that into the rust generated code and calls a backend
function for registering the font that is unimplemented.
