pt-or-px: heed the dpi-aware setting

Before this patch, pt-or-px values, like letter-spacing, were *always*
scaled using the current DPI value.

This is wrong; if the fonts are scaled using the output’s scaling
factor, then so should all other point values.

This also fixes an issue where e.g. letter-spacing would use one DPI
value at startup, but then when increasing/decreasing or resetting the
font size, would be re-calculated using a different DPI value, leading
to completely different spacing.

This happened when there were multiple monitors, with different DPI
values, and foot guessed the initial DPI value wrong. Normally, foot
would correct itself as soon as the window was mapped, and the
“correct” DPI value known. But if the fonts were scaled using the
scaling factor, it was possible that the font reload never happened.

This patch also updates the thickness calculation (for LIGHT and HEAVY
box drawing characters) to use the scaling factor when appropriate.

Closes #680

CHANGELOG.md

@@ -56,6 +56,11 @@
 * Foot now sends `SIGTERM`/`SIGKILL` to the client application’s process group,
   instead of just to the client application’s process.
 * `kmous` terminfo capability from `\E[M` to `\E[<`.
+* pt-or-px values (`letter-spacing`, etc) and the line thickness
+  (`tweak.box-drawing-base-thickness`) in box drawing characters are
+  now translated to pixel values using the monitor’s scaling factor
+  when `dpi-aware=no`, or `dpi-aware=auto` and the scaling factor is
+  larger than 1 (https://codeberg.org/dnkl/foot/issues/680).
 
 
 ### Deprecated