feat: Migrates the layer-transit sample to js-api-samples

[willum070]

This PR does the following things:

• Migrates the layer-transit sample to js-api-samples
• Updates the sample to use gmp-map element and dynamic library loading.

[snippet-bot]

Here is the summary of changes.

You are about to add 3 region tags.

• samples/layer-transit/index.html:7, tag maps_layer_transit
• samples/layer-transit/index.ts:7, tag maps_layer_transit
• samples/layer-transit/style.css:6, tag maps_layer_transit

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