[google_maps] fix markersToChange to actually change modified markers

[KlausJokisuo]

Description

Fixes Marker updating method.
now markers needed to change are actually those which need to be changed

Related Issues

flutter/flutter#27823

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[KlausJokisuo]

I signed it!

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[bogdannedelcu]

Hello @amirh, can you update us on the status on this one please? Thank you.

[KlausJokisuo]

@amirh What is the status of this PR?

[kjeremy]

Why is this taking so long? This is a pretty important performance fix.

[KlausJokisuo]

Is there something I can do to speed up processing of the PR?

[amirh]

@iskakaushik

[amirh]

Left a few comments, Note that multiple tests and presubmits are failing, they will need to be fixed before a PR can be merged.

Generally speaking we are prioritizing issues by the number of thumbs up, so the best way to get it prioritize is to thumb up flutter/flutter#27823. See the review process section.

[KlausJokisuo]

Sorry for the delay!

@iskakaushik
@amirh I've now changed code accordingly to above comments. Thanks for the tip regarding _markersToChange. There is a noticeable performance improvement when changing lot of markers at once.

[bogdannedelcu]

@amirh @iskakaushik can you check if this is ok? We need google map to be as fast as possible. Thanks

[KlausJokisuo]

Fixed in #1933