fix: Adds basic accessibility to routes-markers

[willum070]

This PR makes the following updates to support basic accessibility:

• Adds the title property to route markers to demonstrate adding support for screen readers.
• Makes markers clickable so users can navigate using the tab key and arrow keys.
• Increases the scale of markers for better visibility.

Change-Id: I7373959575fb7b36d7c4b03d9dcc6750705cacb4

[snippet-bot]

Here is the summary of changes.

You are about to add 1 region tag.

• samples/routes-markers/index.ts:83, tag maps_routes_markers_style_maker_intermediate

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