Update Unicode character width determination to support newer versions of Unicode

[meonkeys]

Emoji characters muck up the automatic terminal width detection and cause lines to wrap unexpectedly. Example:

Notice how the final digit in the urgency value appears on the next line.

This screenshot is from taskwarrior v2.5.1 on Ubuntu 20.04.1 64-bit LTS desktop.

Terminal details:

$ gnome-terminal --version
# GNOME Terminal 3.36.2 using VTE 0.60.3 +BIDI +GNUTLS +ICU +SYSTEMD

I think the glyphs are from the fonts-noto-color-emoji package.

[tbabej]

Reproduced on 2.6.0: It looks like we are missing some Unicode characters can take 2 characters in the terminal when expected to only take 1:

Using wcwidth library in Python we can see that this charater's printable length is 2:

>>> from wcwidth import wcwidth
>>> wcwidth('👍')
2

Further investigation shows that this is due to the fact that my chosen character 👍' was defined in Unicode version 6.0, while our current implementation of mk_wcwidth only supports up to version 5.0.

[tbabej]

Indeed, looks like for emojis, the defined length was 1 until Unicode 9.0. The following C++11 header-only library should be a good replacement for the one we're currently using: https://github.com/ridiculousfish/widecharwidth

[tbabej]

Fixed in 2.6.0.