Add new filter command to Package Menu (Bug#39903)

* lisp/emacs-lisp/package.el
(package-menu-filter-marked): New filter command.
* test/lisp/emacs-lisp/package-tests.el
(package-test-list-filter-marked): New test.
(package-menu-mode-menu):
(package-menu-mode-map): Update menu to include new filter command.

* doc/emacs/package.texi (Package Menu): Document the new command.
* etc/NEWS: Announce the new command.

1 files changed, 1 insertions, 0 deletions

diff --git a/etc/NEWS b/etc/NEWS
index 12406eea822..ae676a9bf83 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -219,6 +219,7 @@ key             binding
 / n             package-menu-filter-by-name
 / s             package-menu-filter-by-status
 / v             package-menu-filter-by-version
+/ m             package-menu-filter-marked
 / /             package-menu-filter-clear
 
 ** gdb-mi