move issue filters to shared template (#25729)

Issue filters are being used on repo list page and on milestone issues
page, and the code is mostly duplicated.

This PR does the following changes:
- move issue filters into a shared template
- allow filtering milestone issues by project, so no need to hide this
filter on milestone issues page
- remove some dead code (e. g. issue actions in milestone issues
template)
- fix label filter dropdown width

---------

Co-authored-by: 6543 <6543@obermui.de>

web_src/css/repo/issue-list.css

@@ -1,6 +1,6 @@
 .issue-list-toolbar {
   display: flex;
-  flex-wrap: wrap;
+  flex-wrap: wrap-reverse;
   justify-content: space-between;
   align-items: flex-start;
   gap: 1rem;
@@ -14,13 +14,9 @@
 .issue-list-toolbar-right .filter.menu {
   flex-direction: row;
   flex-wrap: wrap;
-  gap: 8px;
 }
 
 @media (max-width: 767.98px) {
-  .issue-list-toolbar {
-    flex-direction: column-reverse;
-  }
   .issue-list-toolbar-right .dropdown .menu {
     left: auto !important;
     right: auto !important;