dap-mode: set extensions variable to doom-cache
dap-mode: set extensions variable to doom-cache

Previously, this would put the .extension directory in
`user-emacs-directory' which in doom's case will be in the root of the
doom directory.

So, we move the directory to doom's etc dir and also name it something
descriptive instead of 'extension'.

UndeadKernel/emacs_doom,hlissner/.emacs.d,UndeadKernel/emacs_doom,hlissner/doom-emacs,hlissner/.emacs.d,hlissner/doom-emacs,hlissner/doom-emacs,hlissner/.emacs.d,hlissner/doom-emacs,UndeadKernel/emacs_doom,hlissner/doom-emacs,UndeadKernel/emacs_doom,hlissner/.emacs.d,hlissner/doom-emacs,hlissner/.emacs.d,hlissner/doom-emacs,hlissner/.emacs.d,hlissner/.emacs.d,UndeadKernel/emacs_doom,hlissner/.emacs.d,UndeadKernel/emacs_doom,UndeadKernel/emacs_doom