font(fix): Extract and apply Nerd Font codepoint mapping table (#9142)

Fixes #9076

**Before** 
<img width="128" height="57" alt="Screenshot 2025-10-11 at 00 07 09"
src="https://github.com/user-attachments/assets/a6b416d5-dae1-4cea-a836-00640ceaf39b"
/>

**After**
<img width="128" height="57" alt="Screenshot 2025-10-11 at 00 07 31"
src="https://github.com/user-attachments/assets/7d2df7b1-4767-4e2d-84d2-8301da5c6602"
/>

These screenshots show the chevrons mentioned in
https://github.com/ghostty-org/ghostty/discussions/7820#discussioncomment-14617170,
which should be scaled as a group but were not until this PR.

The added code downloads each individual symbol font file from the Nerd
Fonts github repo (making sure to get the version corresponding to the
vendored `font-patcher.py`) and iterates over all of them to build the
correct and complete codepoint mapping table. The table is saved to
`nerd_font_codepoint_tables.py`, which `nerd_font_codegen.py` will reuse
if possible instead of downloading the font files again.

I'm not going to utter any famous last words or anything, but... after
this, I don't think the number of remaining issues with icon
scaling/alignment is _large._

0 files changed, 0 insertions, 0 deletions