"maint test-settings set/show" -> "maint set/show test-settings"

"maint test-settings set/show" -> "maint set/show test-settings"

This commit renames "maint test-settings set/show" to "maint set/show
test-settings".

This helps the following patch, which introduce a "maint with" command
what works with all "maint set" settings.

gdb/ChangeLog:
2019-07-03  Pedro Alves  <palves@redhat.com>

	* NEWS (New commands): Mention "maint set/show test-settings"
	instead of "maint test-settings".
	* maint-test-settings.c (maintenance_test_settings_list): Delete.
	(maintenance_test_settings_set_list): Rename to ...
	(maintenance_set_test_settings_list): ... this.
	(maintenance_test_settings_show_list): Rename to  ...
	(maintenance_show_test_settings_list): ... this.
	(maintenance_test_settings_cmd): Delete.
	(maintenance_test_settings_set_cmd): ...
	(maintenance_set_test_settings_cmd): ... this.
	(maintenance_test_settings_show_cmd): ...
	(maintenance_show_test_settings_cmd): ... this.
	(maintenance_test_settings_show_value_cmd):
	(maintenance_show_test_settings_value_cmd): ... this.
	(_initialize_maint_test_settings): No longer install the "maint
	test-settings" prefix command.  Rename "maint test-settings set"
	to "maint set test-settings", and "maint test-settings show" to
	"maint show test-settings".  Adjust all subcommands.

gdb/doc/ChangeLog:
2019-07-03  Pedro Alves  <palves@redhat.com>

	* gdb.texinfo (Maintenance Commands): Document "maint set/show
	test-settings" instead of "maint test-settings set/show".

gdb/testsuite/ChangeLog:
2019-07-03  Pedro Alves  <palves@redhat.com>

	* gdb.base/settings.exp: Replace all references to "maint
	test-settings set" with references to "maint set test-settings",
	and all references to "maint test-settings show" with references
	to "maint show test-settings".