Ensure that gud commands for M-x gdb are handled by repeat-mode

Ensure that gud commands for M-x gdb are handled by repeat-mode

* lisp/progmodes/gud.el (gud-gdb-repeat-map): Rename from
gud-repeat-map, and populate at the top-level.
(gud-set-repeat-map-property): Introduce this helper function for
setting the repeat-map property.
(gud-gdb): Use the gud-set-repeat-map-property function to assign the
repeat-map property.

* lisp/progmodes/gdb-mi.el (gdb): Use the gud-set-repeat-map-property
function to assign the repeat-map property.

Because different debugging tools may not support all of the gud-foo
functions, we reassign the repeat-map property within the respective
commands, as opposed to the top level of the files, to ensure that the
repeat-map property is reassigned each time to a symbol corresponding
to the active debugging tool.  (Bug#49632)