Add types to package.json exports

[chrispawley]

Using this package with the latest default angular tsconfig, which uses 'moduleResolution: bundler' i got this typescript error:

Could not find a declaration file for module '@googlemaps/adv-markers-utils'
There are types at '@googlemaps/adv-markers-utils/dist/index.d.ts', but this result could not be resolved when respecting package.json "exports".

Updating package.json imports format resolved this issue.

from:

"import": "./dist/index.modern.js,"

to:

"import": { "types": "./dist/index.d.ts", "default": "./dist/index.modern.js" }

🦕

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