fix(Metal): fix crunchy appearance of constrained glyphs

We can't use nearest neighbor filtering for sampling from the atlas
because we might not actually be doing pixel perfect sampling if the
glyph has been constrained. This will change in the future, but this
will have to be set to linear for now.

src/renderer/shaders/cell.metal

@@ -499,7 +499,11 @@ fragment float4 cell_text_fragment(
   constexpr sampler textureSampler(
     coord::pixel,
     address::clamp_to_edge,
-    filter::nearest
+    // TODO(qwerasd): This can be changed back to filter::nearest when
+    //                we move the constraint logic out of the GPU code
+    //                which should once again guarantee pixel perfect
+    //                sizing.
+    filter::linear
   );
 
   switch (in.mode) {