[Feature Request]: Add check for Customizer

[tyrann0us]

Is your feature request related to a problem?

Currently, it is not possible to check whether the current request is from the Customizer.

Describe the desired solution

Add a ->is(WpContext::CUSTOMIZER)/->isCustomizer() check.

Describe the alternatives that you have considered

The Customizer is gradually being replaced by FSE, so it will eventually cease to exist. The question is whether new logic should be introduced for a "legacy" feature.

Additional context

Without this feature, you have to cumbersome check for the Customizer yourself:

global $wp_customize;
if (isset($wp_customize)) {
    // do things
}

Code of Conduct

• I agree to follow this project's Code of Conduct

[widoz]

This would also include something like isCustomizePreview ? The customizer is composed of two parts the Panels and the Preview.

[lkraav]

Customize will be around for long enough (years), I think yes, this request type availability is warranted for a while.