fix: fixed theme flash on page load

[faustinozanetto]

Description

This PR introduces a simple fix for addressing the theme flashing that is noticeable when the page loads. It uses a custom script that mimics the setCurrentTheme function in the legacyMain.js script but directly injects into the head element. This way, the page does not need to wait for the legacyMain.js script to load to apply the theme as the script is already in the html response.

Validation

To ensure this fix works you can either do a simple page refresh, or head to the Performance tab in the developer tools and perform a profiler start with page refresh and see that there is no theme flash present.

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Name	Status	Preview	Comments	Updated (UTC)
nodejs-org	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Aug 9, 2023 3:05pm

[ovflowd]

I appreciate the effort, but we're not accepting changes against the current Node.js website right now, as we're in the process of working towards a redesign.

I would also be heavily against injected scripts with dangerouslySetInnerHTML

Read more about current efforts at #5131

[faustinozanetto]

I appreciate the effort, but we're not accepting changes against the current Node.js website right now, as we're in the process of working towards a redesign.

I would also be heavily against injected scripts with dangerouslySetInnerHTML

Read more about current efforts at #5131

Regards the script injection, next themes also uses that so maybe in the upcoming rework they should replace it with something else.