put paperclip in send file button

src/platform/web/ui/css/themes/element/icons/paperclip.svg

@@ -0,0 +1,3 @@
+<svg width="20" height="20" viewBox="0 0 20 20" fill="none" xmlns="http://www.w3.org/2000/svg">
+<path d="M18.099 9.51084L10.4407 17.1692C8.48696 19.1229 5.31938 19.1229 3.36567 17.1692C1.41196 15.2155 1.41196 12.0479 3.36567 10.0942L11.024 2.43584C12.3265 1.13337 14.4382 1.13337 15.7407 2.43584C17.0431 3.73831 17.0431 5.85003 15.7407 7.1525L8.074 14.8108C7.42277 15.4621 6.36691 15.4621 5.71567 14.8108C5.06444 14.1596 5.06444 13.1037 5.71567 12.4525L12.7907 5.38584" stroke="#61708B" stroke-linecap="round" stroke-linejoin="round"/>
+</svg>

src/platform/web/ui/css/themes/element/theme.css

@@ -470,6 +470,20 @@ a {
     background-position: center;
 }
 
+.MessageComposer > button.sendFile {
+    width: 32px;
+    height: 32px;
+    display: block;
+    border: none;
+    text-indent: 200%;
+    white-space: nowrap;
+    overflow: hidden;
+    background-color: transparent;
+    background-image: url('icons/paperclip.svg');
+    background-repeat: no-repeat;
+    background-position: center;
+}
+
 .MessageComposer > button.send:disabled {
     background-color: #E3E8F0;
 }

src/platform/web/ui/session/room/MessageComposer.js

@@ -31,10 +31,10 @@ export class MessageComposer extends TemplateView {
         return t.div({className: "MessageComposer"}, [
             this._input,
             t.button({
-                className: "attach",
-                title: vm.i18n`Attach`,
+                className: "sendFile",
+                title: vm.i18n`Send file`,
                 onClick: () => vm.sendAttachment(),
-            }, vm.i18n`Attach`),
+            }, vm.i18n`Send file`),
             t.button({
                 className: "send",
                 title: vm.i18n`Send`,