Separate bootloader and firmware fonts

[obrusvit]

As of #4536, (and #4536 (comment)) we moved from enum Font to type Font = &'static FontInfo. For convenience, in the older enum approach, some fonts were mapped to the same enum variant during build, e.g. for TS3 (Caesar UI):

    if stage == "bootloader":
        # ...
        font_big = "Font_PixelOperator_Regular_8"
    if stage == "firmware":
        #...
        font_big = "Font_Unifont_Regular_16"

This was done so that:

• there were less fonts for bootloader (to preserve flash size)
• using hardcoded font in components was possible, e.g.

let font = Font::FONT_BIG;   // using Font_Unifont_Regular_16 in Firmware but Font_PixelOperator_Regular_8 in Bootloader

In order to preserve the code without too much refactoring a crutch was made in this manner in #4536:

// same for both FW and BL
pub const FONT_NORMAL: crate::ui::display::Font = &Font_PixelOperator_Regular_8_info;

#[cfg(feature = "bootloader")]
pub const FONT_BIG: crate::ui::display::Font = FONT_NORMAL;
#[cfg(not(feature = "bootloader"))]
pub const FONT_BIG: crate::ui::display::Font = &Font_Unifont_Regular_16_info;

---

This task is to improve it so that:

• bootloader code only uses the fonts it's supposed to have (others might be feature-gated),
• components which use specific Font rather take it as a parameter,
• (optionally) theme/mod.rs is split into theme/mod.rs (common) and theme/firmware.rs.