feat: Migrates DDS boundaries-simple sample; quality and standards.

[willum070]

This PR migrates boundaries-simple to js-api-samples, and makes the following changes:

• Updates the sample to use the gmp-map element.
• Minor cleanup (removed some ts-ignores, simplified import statement).

[snippet-bot]

Here is the summary of changes.

You are about to add 5 region tags.

• samples/boundaries-simple/index.html:7, tag maps_boundaries_simple
• samples/boundaries-simple/index.ts:12, tag maps_boundaries_simple
• samples/boundaries-simple/index.ts:27, tag maps_boundaries_simple_get_layer
• samples/boundaries-simple/index.ts:32, tag maps_boundaries_simple_style_single
• samples/boundaries-simple/style.css:6, tag maps_boundaries_simple

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