Enqueue scripts using plugins_url() instead of plugin_dir_url()

[SohamPatel46]

Summary

Fixes #1647

Relevant technical choices

• Update all instances of plugin_dir_url() function to plugins_url() function, because the latter one is more appropriate to use whenever we want a path appended at the end of the URL.
• Updated all 7 instances found in 6 files - https://github.com/search?q=repo%3AWordPress%2Fperformance%20plugin_dir_url&type=code

[github-actions]

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Co-authored-by: SohamPatel46 <sohampate1@git.wordpress.org>
Co-authored-by: felixarntz <flixos90@git.wordpress.org>
Co-authored-by: westonruter <westonruter@git.wordpress.org>

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[SohamPatel46]

Hello, Can someone with access can add the required labels ? I dont seem to have enough access to do that.

[westonruter]

LGTM