[web] Fix image getting evicted after being consumed from CrossFrameCache

[ferhatb]

Description

When SceneBuilder repaints pictures and PersistedPicture reuses a recycled BitmapCanvas, multiple BitmapCanvas's can point to same element cache. After a frame is painted, the cache evicts unused images although they get used by another Picture applyBitmapPaint. This PR makes sure elementCache is cleared when recycling a BitmapCanvas for future use.

Related Issues

flutter/flutter#60460

Tests

Added a test to make sure same image is reused across updates.

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Breaking Change

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[yjbanov]