This adds nt, sp, and ft as aliases for new-tab, split-pane,
and focus-tab, respectively. These do exactly the same thing as their
long for counterparts, but are just shorter, for those of us who type
slower than a fifth grader 👀

Now you can do

wt nt cmd.exe /k #work 15 ; sp cmd.exe /k #work 15 ; sp cmd.exe /k
media-commandline ; nt powershell dev\\symbols.ps1 ; nt -p \"Ubuntu\" ;
nt -p \"Ubuntu\" ; ft -t 0

instead of

new-tab cmd.exe /k #work 15 ; split-pane cmd.exe /k #work 15 ;
split-pane cmd.exe /k media-commandline ; new-tab powershell
dev\\symbols.ps1 ; new-tab -p \"Ubuntu\" ; new-tab -p \"Ubuntu\" ;
focus-tab -t 0

The pattern I'm using here is that each of these subcommands now has a
little helper lambda that actually sets up the subcommand with the
required arguments, and we just call that lambda twice, once for the
long-form of the command, and again for the short.

I imagine that in the future, we won't necessarily have short-forms for
every subcommands, so if there are future conflicts we'd have to figure
that out pre-emptively, but these all seem like they'll need a short
form.

Closes #5466