Add store/restore window configuration feature for gdb-mi

Add store/restore window configuration feature for gdb-mi

Add a feature that allows a user to save a gdb window
configuration (window layout) to a file with
'gdb-save-window-configuration' and load it back with
'gdb-load-window-configuration'.  Set a default window configuration
by setting 'gdb-default-window-configuration-file'.
Add an option to make gdb preserve the window configuration
that the user had before starting gdb.  In window.el, add
'with-window-non-dedicated'.

* lisp/progmodes/gdb-mi.el (top/level): Require 'pcase' and 'cl-seq'.
(gdb--window-configuration-before): New variable.
(gdb-restore-window-configuration-after-quit): New option.
(gdb-window-configuration-directory,
gdb-default-window-configuration-file): New variables.
(gdb): Save configuration on startup.
(gud-menu-map): Add "Load Layout" and "Save Layout" to menu.  Add
"Restore Layout After Quit" button to menu.  Rename "Restore Window
Layout" to "Restore Default Layout", add some help echo, and move it
from "GDB-MI" menu to "GDB-WINDOWs" menu.
(gdb-toggle-restore-window-configuration): New function.
(gdb-get-source-buffer): New function, extracted out of
'gdb-restore-window'.
(gdb-setup-windows): Add a condition branch that loads default window
configuration when available.  Fix docstring.
(gdb-buffer-p, gdb-function-buffer-p, gdb--buffer-type,
gdb-save-window-configuration, gdb-load-window-configuration): New
functions.
(gdb-restore-windows): Edit docstring to mention
'gdb-default-window-configuration-file'.
(gdb-reset): Restore window configuration after quit.
* lisp/window.el (with-window-non-dedicated): New macro.