room-history: Increase message line height

Unfortuntely line height on multi-height labels is way too tight by default in GTK4, so we need to work around it in apps.
One very visible instance of this is the message bodies in the timeline.

I fixed issue by adding css line-height property on .room-history row css class.

https://gitlab.gnome.org/GNOME/fractal/-/issues/1030

Part-of: <https://gitlab.gnome.org/GNOME/fractal/-/merge_requests/1141>

data/resources/style.css

@@ -9,6 +9,10 @@ textview, text {
   font-weight: bold;
 }
 
+.line-height {
+  line-height: 150%;
+}
+
 button.pill.large {
   padding: 12px 40px;
 }

src/components/label_with_widgets.rs

@@ -96,6 +96,7 @@ mod imp {
             label.set_wrap_mode(pango::WrapMode::WordChar);
             label.set_xalign(0.0);
             label.set_valign(gtk::Align::Start);
+            label.add_css_class("line-height");
             label.connect_notify_local(
                 Some("label"),
                 clone!(@weak obj => move |_, _| {