tools (common/template): add brands style in icon definitions:

`brands` is notably needed for the new XMPP icon available in font-awesome.

libervia/backend/tools/common/template.py

@@ -1032,16 +1032,15 @@ class Renderer:
         for name in names:
             if "/" in name:
                 raise ValueError("SVG name must not have a `/` in it.")
-            if name.startswith("regular "):
-                filename = name[8:]
-                path = self.fa_svgs_path / f"regular/{filename}.svg"
+            for style_name in ("regular", "brands", "solid"):
+                if name.startswith(f"{style_name} "):
+                    style = style_name
+                    filename = name.removeprefix(f"{style_name} ")
+                    break
             else:
-                if name.startswith("solid "):
-                    # "solid" can be explicitely specified, and it's the default value.
-                    filename = name[6:]
-                else:
-                    filename = name
-                path = self.fa_svgs_path / f"solid/{filename}.svg"
+                style = "solid"
+                filename = name
+            path = self.fa_svgs_path / f"{style}/{filename}.svg"
 
             # Parse the source SVG
             try: