[vector_graphics] Add auto mode for vector_graphic:

Auto mode generates the appropriate raster cache for the current drawing size to reduce the overhead of subsequent RenderPass executions. If the cache is not created or is too large, it will automatically fall back to picture mode for real-time rendering.

Author: gaodi-sec

packages/vector_graphics/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 1.2.0
+
+* Add an auto render strategy to reduce Impeller engine rendering overhead.
+
 ## 1.1.18
 
 * Allow transition between placeholder and loaded image to have an animation.