These arrows were previously drawn using the code points U+2B06 and
U+2B07. The .png files for these emoji were removed in commit bfe99eb
and added to the Katica Regular 10 font in commit cf62d08. The emoji
were not added to the bold Katica variants that are used by the table
header view. The effect is that a "?" replacement character was
rendered.
Instead of rendering the emoji, we can draw the arrows programatically,
like we do in other GUI components (e.g. the scrollbar).
SPDX License Identifiers are a more compact / standardized
way of representing file license information.
See: https://spdx.dev/resources/use/#identifiers
This was done with the `ambr` search and replace tool.
ambr --no-parent-ignore --key-from-file --rep-from-file key.txt rep.txt *
Columns can now be best-fit resized by double-clicking their
grabbable edges. When a default width is set and all data is empty,
double-clicking will restore the column to its original state.
