Improve issue list filter (#24425)

Partial regression of #24393, not only regression, but broken for long
time, 24393 didn't really improve it but used wrong `overflow: scroll`.

Actually, that "ui secondary filter menu labels" shouldn't be set as
scrollable (I missed that at that time), the problem is: if a "ui menu"
has "dropdown" items, then it should not be scrollable. Otherwise the
dropdown menu can't be shown correctly.

And there are more problems:

* The "issue-filters" shouldn't be used anywhere else (copying&pasting
problem again ....)
* There is also an "issue-actions" container, it should also be fixed.
* There are similar problems on the milestone page.
* The old comment in code: "grid column" doesn't work well.

The major changes of this PR are: use "flex: 1" instead of "ui grid
column".

After this PR, not 100% perfect but much better than before.

web_src/css/index.css

@@ -32,6 +32,7 @@
 @import "./repository.css";
 @import "./repository/release-tag.css";
 @import "./repository/issue-label.css";
+@import "./repository/issue-list.css";
 @import "./repository/list-header.css";
 @import "./editor.css";
 @import "./editor/combomarkdowneditor.css";

web_src/css/repository.css

@@ -141,12 +141,19 @@
   font-size: 11px;
 }
 
-.repository .filter.menu .menu {
+/* make all issue filter dropdown menus popup leftward, to avoid go out the viewport (right side) */
+.repository .filter.menu .ui.dropdown .menu {
   max-height: 500px;
   max-width: 300px;
   overflow-x: hidden;
-  right: 0 !important;
-  left: auto !important;
+  right: 0;
+  left: auto;
+}
+
+/* the label-filter is the first dropdown, it shouldn't be shown leftward, otherwise it may go out the viewport (left side) */
+.repository .filter.menu .ui.dropdown.label-filter .menu {
+  right: unset;
+  left: 0;
 }
 
 .repository .select-label .desc {
@@ -2394,10 +2401,6 @@
   margin: 6px 0;
 }
 
-#issue-actions {
-  margin-top: -1rem !important; /* counteract padding from Semantic */
-}
-
 .ui.menu .item > img:not(.ui) {
   width: auto;
 }

web_src/css/repository/issue-list.css

@@ -0,0 +1,14 @@
+.issue-list-toolbar {
+  display: flex;
+  flex-wrap: wrap;
+  align-items: flex-start;
+  gap: 1rem;
+}
+
+.issue-list-toolbar-left {
+  display: flex;
+}
+
+.issue-list-toolbar-right {
+  margin-left: auto;
+}