feat: Migrates the control-custom-state sample.

[willum070]

This PR makes the following changes:

• Migrates the control-custom-state sample to js-api-samples.
• Refactors the sample to use the gmp-map element and dynamic loading.
• Refactors the UI to be declarative, resulting in a much simpler sample.

[snippet-bot]

Here is the summary of changes.

You are about to add 4 region tags.

• samples/control-custom-state/index.html:7, tag maps_control_custom_state
• samples/control-custom-state/index.ts:7, tag maps_control_custom_state
• samples/control-custom-state/index.ts:22, tag maps_control_custom_state_event_listeners
• samples/control-custom-state/style.css:6, tag maps_control_custom_state

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