Add toy variable-width stroker sample

- Currently supports single-segment paths (lines or quads). Doesn't
  handle joins.
- Cubics are easy to add but not supported yet.
- No effort was made on performance optimization.
- Will likely be relocated eventually into an experimental SkPathEffect.

Change-Id: I35073d1d9dbc03a5423fda3bb20da005964c97d6
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/329256
Reviewed-by: Chris Dalton <csmartdalton@google.com>
Commit-Queue: Tyler Denniston <tdenniston@google.com>
diff --git a/BUILD.gn b/BUILD.gn
index f0231c7..6641068 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -1941,6 +1941,7 @@
       "modules/skparagraph:samples",
       "modules/skshaper",
       "modules/svg",
+      "//third_party/imgui",
     ]
   }
   test_lib("hash_and_encode") {