Add colors to Proced (bug#59407)

Add colors to Proced (bug#59407)

Add a new custom variable proced-enable-color-flag which when set to a
non-nil value (defaults to nil), will prompt some format functions to
furnish their respective process attributes with colors and effects in
order to make them easier to distinguish and highlight possible issues
(e.g. high memory usage), in a manner similar to htop.

In particular, the current Emacs process id is highlighted purple in
both the process id and parent process id columns, session leaders
have their process ids underlined, larger memory sizes for rss
are highlighted in darker shades of orange, and the first word in the
args property (the executable) is highlighted in blue.

* lisp/proced.el (proced-grammar-alist): Update to use the new format
functions.
(proced-low-memory-usage-threshold): New custom variable to determine
whether a value represents 'low' memory usage, used only in
proced-format-memory for coloring.
(proced-medium-memory-usage-threshold): New custom variable to
determine whether a value represents 'medium' memory usage, used only
in proced-format-memory for coloring.
(proced-enable-color-flag): New custom variable to toggle coloring.
(proced-run-status-code, proced-interruptible-sleep-status-code)
(proced-uninterruptible-sleep-status-code, proced-executable)
(proced-executable, proced-memory-gb, proced-memory-mb)
(proced-memory-default, proced-pid, proced-ppid, proced-pgrp)
(proced-sess, proced-cpu, proced-mem, proced-user, proced-time-colon):
New faces.
(proced-format-time): Edit function to color colons using
proced-time-colon.
(proced-format-args): Edit function to color executables using
proced-executable.
(proced-format-state): New function to color states.
(proced-format-pid): New function to color process ids.
(proced-format-ppid): New function to color parent process ids.
(proced-format-pgrp): New function to color process group ids.
(proced-format-sess): New function to color process session leader
ids.
(proced-format-cpu): New function to color cpu utilization.
(proced-format-mem): New function to color memory utilization.
(proced-format-user): New function to color the user a process
belongs to.