HaikuDepot TextView: simple implementation of underlined text

The TextView has planned support for fancy underlines (double underline,
squiggly, and possibly different colors than the text). However, it does
not implement any rendering for these yet. Until that is added, have at
least the basic case (single line underline the same color as the text)
by using BFont B_UNDERSCORE_FACE flag.

Change-Id: I26875e51efb1050cbabb2287307516c4cea077cf
Reviewed-on: https://review.haiku-os.org/c/haiku/+/7129
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>
Reviewed-by: Adrien Destugues <pulkomandy@pulkomandy.tk>

HaikuDepot: remove unneeded .Get() calls

Dereference operator is defined in BReference.

Change-Id: Iccba8ad4a29e354aa9cdbf2e1a5ddbc9687af677
Reviewed-on: https://review.haiku-os.org/c/haiku/+/3489
Reviewed-by: Adrien Destugues <pulkomandy@gmail.com>

use .IsSet() instead if .Get() != NULL

Change-Id: Ia2b7a719fd398e78cc3b11d4f7b02cb81179f65f
Reviewed-on: https://review.haiku-os.org/c/haiku/+/3488
Reviewed-by: Jérôme Duval <jerome.duval@gmail.com>

apps: Convert to using Set*UIColor.

Signed-off-by: Augustin Cavalier <waddlesplash@gmail.com>
Patches 0045-0075, 0077-0087 from looncraz, unmodified.

Renamed HaikuDepot's home to haikudepot.

* This closes #10699. I mentioned that to stippi after his first commit
of HaikuDepot, anyway :-)

Renamed HaikuDepot's home to haikudepot.

* This closes #10699. I mentioned that to stippi after his first commit
of HaikuDepot, anyway :-)