Unify grid metrics calculations by relying on shared logic mostly based
on values directly from the font tables, this deduplicates a lot of code
and gives us more control over how we interpret various metrics.
Also separate metrics for underlined, strikethrough, and overline
thickness and position, and box drawing thickness, so that they can
individually be adjusted as the user desires.
Fixes#2364
This adds the bold, italic, and bold italic variants of JB Mono so it is
built-in. This also fixes up the naming convention for the embedded font
files across tests and removes redundant embedded font files.
Fixes#1722
Previously, SharedGrid.getIndex would properly lock any access to search
for and load the face metadata for a font face that contains a
codepoint. However, that face may be "deferred" (metadata loaded but the
actual face not loaded).
Later, outside of the SharedGrid write lock, a deferred face may be
initialized and cause a data race if two threads are doing this at the
same time, sometimes loading to a crash.
This commit fixes the issue by always preloading font indexes in
getIndex because the usage of getIndex implies a very near term future
use of getFace.
