fix(core): Ensure there's only one global spotlight event target

[Lms24]

This is sort of a workaround for #68 which should ensure that even if two spotlight bundle variants end up in the build, still the same event target is used for communication. Not ideal and I'd like to revisit this but for now it should permit opening spotlight in astro apps again (🤞)

This change puts the eventTarget of spotlight onto the global window, thereby ensuring that all bundles get the same instance of the target.

Ideally, we find a way to avoid the double bundling un Astro but we might still keep this around. I have the feeling that something like this could occur in other framework/bundler combinations.

[vercel]

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Name	Status	Preview	Comments	Updated (UTC)
spotlightjs	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Nov 22, 2023 10:52pm

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (e3f88d1) 30.85% compared to head (3877f38) 30.85%.
Report is 3 commits behind head on main.

❗ Current head 3877f38 differs from pull request most recent head 30e5e94. Consider uploading reports for the commit 30e5e94 to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #121   +/-   ##
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  Coverage   30.85%   30.85%           
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  Files          30       30           
  Lines        1465     1465           
  Branches       48       48           
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  Hits          452      452           
  Misses       1013     1013           

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