Fix text selection in dropdown list items

Explicitly enables text selection within dropdown menu items and
prevents the menu from automatically closing when attempting to
highlight text. The keep-open attribute detaches native auto-close
behavior, while the click handler intercepts text selection.

Google-Bug-Id: b/483219058
Release-Notes: skip
Change-Id: I5b87693cf1910c9ee0d991dd86bf4e7cba5f6c8e

polygerrit-ui/app/elements/shared/gr-dropdown-list/gr-dropdown-list.ts

diff --git a/polygerrit-ui/app/elements/shared/gr-dropdown-list/gr-dropdown-list.ts b/polygerrit-ui/app/elements/shared/gr-dropdown-list/gr-dropdown-list.ts
index 4eaf3a8..4e65b99 100644
--- a/polygerrit-ui/app/elements/shared/gr-dropdown-list/gr-dropdown-list.ts
+++ b/polygerrit-ui/app/elements/shared/gr-dropdown-list/gr-dropdown-list.ts
@@ -138,6 +138,10 @@
           --md-divider-color: var(--border-color);
         }
         md-menu-item {
+          -moz-user-select: text;
+          -ms-user-select: text;
+          -webkit-user-select: text;
+          user-select: text;
           max-height: 70vh;
           min-width: 266px;
           --md-sys-color-on-surface: var(
@@ -368,10 +372,16 @@
   private renderMdMenuItem(item: DropdownItem, index: number) {
     return html`
       <md-menu-item
+        keep-open
         ?selected=${this.value === String(item.value)}
         ?active=${this.value === String(item.value)}
         ?disabled=${!!item.disabled}
-        @click=${() => {
+        @click=${(e: Event) => {
+          if (document.getSelection()?.toString().length !== 0) {
+            e.preventDefault();
+            e.stopPropagation();
+            return;
+          }
           this.value = String(item.value);
         }}
         @keydown=${(e: KeyboardEvent) => {
@@ -483,6 +493,9 @@
    */
   private handleDropdownClick() {
     assertIsDefined(this.dropdown);
+    if (document.getSelection()?.toString().length !== 0) {
+      return;
+    }
 
     this.dropdown.close();
   }

polygerrit-ui/app/elements/shared/gr-dropdown-list/gr-dropdown-list_test.ts

diff --git a/polygerrit-ui/app/elements/shared/gr-dropdown-list/gr-dropdown-list_test.ts b/polygerrit-ui/app/elements/shared/gr-dropdown-list/gr-dropdown-list_test.ts
index 6b888ff..5fb5ffc 100644
--- a/polygerrit-ui/app/elements/shared/gr-dropdown-list/gr-dropdown-list_test.ts
+++ b/polygerrit-ui/app/elements/shared/gr-dropdown-list/gr-dropdown-list_test.ts
@@ -81,7 +81,7 @@
               quick=""
               tabindex="-1"
             >
-              <md-menu-item md-menu-item="" tabindex="0">
+              <md-menu-item keep-open="" md-menu-item="" tabindex="0">
                 <div class="topContent">
                   <div>
                   <span class="desktopText">
@@ -93,7 +93,7 @@
                 </div>
               </md-menu-item>
               <md-divider role="separator" tabindex="-1"> </md-divider>
-              <md-menu-item active="" md-menu-item="" selected="" tabindex="-1">
+              <md-menu-item active="" keep-open="" md-menu-item="" selected="" tabindex="-1">
                 <div class="topContent">
                   <div>
                   <span class="desktopText">
@@ -107,7 +107,7 @@
                 </div>
               </md-menu-item>
               <md-divider role="separator" tabindex="-1"> </md-divider>
-              <md-menu-item disabled="" md-menu-item="" tabindex="-1">
+              <md-menu-item disabled="" keep-open="" md-menu-item="" tabindex="-1">
                 <div class="topContent">
                   <div>
                   <span class="desktopText">