Fix point annotation update bitmap affect others issue.

[Chaoba]

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Fixes: #587

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Summary of changes

This pr changes the way to generate iconImage value for PointAnnotation and update the check condition for updating bitmap.

device-2021-09-10-155401.mp4

User impact (optional)

[kiryldz]

Shouldn't we revisit how generationId is generated instead of not using it here and introducing standard hash function?

[Chaoba]

From the official docs: generationId changes whenever the bitmap is modified. This can be used as an efficient way to check if a bitmap has changed. Here we want to distinguish different bitmap, so use hashCode would be appropriate.