Vectorize spinners

This replaces most of the GIF spinners used throughout the app with an
SVG that respects the user's theme. However, spinner.gif is still
retained for the room timeline avatar uploader component, since it is
more difficult to replace.

Signed-off-by: Robin Townsend <robin@robin.town>

res/css/views/elements/_InlineSpinner.scss

@@ -18,7 +18,24 @@ limitations under the License.
     display: inline;
 }
 
-.mx_InlineSpinner_spin img {
+.mx_InlineSpinner img, .mx_InlineSpinner_icon {
     margin: 0px 6px;
     vertical-align: -3px;
 }
+
+@keyframes spin {
+    from {
+        transform: rotateZ(0deg);
+    }
+    to {
+        transform: rotateZ(360deg);
+    }
+}
+
+.mx_InlineSpinner_icon {
+    display: inline-block;
+    background-color: $primary-fg-color;
+    mask: url('$(res)/img/spinner.svg');
+    mask-size: contain;
+    animation: 1.1s steps(12, end) infinite spin;
+}

res/css/views/elements/_Spinner.scss

@@ -26,3 +26,19 @@ limitations under the License.
 .mx_MatrixChat_middlePanel .mx_Spinner {
     height: auto;
 }
+
+@keyframes spin {
+    from {
+        transform: rotateZ(0deg);
+    }
+    to {
+        transform: rotateZ(360deg);
+    }
+}
+
+.mx_Spinner_icon {
+    background-color: $primary-fg-color;
+    mask: url('$(res)/img/spinner.svg');
+    mask-size: contain;
+    animation: 1.1s steps(12, end) infinite spin;
+}