refactor(font): move ownership of Metrics to Collection

This sets the stage for dynamically adjusting the sizes of fallback
fonts based on the primary font's face metrics. It also removes a lot of
unnecessary work when loading fallback fonts, since we only actually use
the metrics based on the parimary font.

src/font/SharedGrid.zig

@@ -111,15 +111,10 @@ pub fn deinit(self: *SharedGrid, alloc: Allocator) void {
 }
 
 fn reloadMetrics(self: *SharedGrid) !void {
-    // Get our cell metrics based on a regular font ascii 'M'. Why 'M'?
-    // Doesn't matter, any normal ASCII will do we're just trying to make
-    // sure we use the regular font.
-    // We don't go through our caching layer because we want to minimize
-    // possible failures.
     const collection = &self.resolver.collection;
-    const index = collection.getIndex('M', .regular, .{ .any = {} }).?;
-    const face = try collection.getFace(index);
-    self.metrics = face.metrics;
+    try collection.updateMetrics();
+
+    self.metrics = collection.metrics.?;
 
     // Setup our sprite font.
     self.resolver.sprite = .{ .metrics = self.metrics };