[PaintWorklet] Explicitly state the PaintSize could be fractional

Author: xidachen

css-paint-api/Overview.bs

@@ -421,7 +421,7 @@ is treated as opaque black.
 When the user agent is to <dfn>create a PaintRenderingContext2D object</dfn> for a given |width|,
 |height|, and |paintRenderingContext2DSettings|, it <em>must</em> run the following steps:
     1. Create a new {{PaintRenderingContext2D}}.
-    2. <a>Set bitmap dimensions</a> for the context's <a>output bitmap</a> to |width| and |height|.
+    2. <a>Set bitmap dimensions</a> for the context's <a>output bitmap</a> to the rounded values of |width| and |height|.
     3. Set the {{PaintRenderingContext2D}}'s <a>alpha</a> flag to |paintRenderingContext2DSettings.alpha|.
     4. Return the new {{PaintRenderingContext2D}}.