NavigatorProvider: Exclude size value from contain CSS rule

[t-hamano]

Fixes #57494
Related to #56909

What?

This PR excludes the size value by changing the value of the contain CSS property applied to the NavigatorProvider component from strict (equivalent to size layout paint style) to content (equivalent to layout paint style).

As a result, this PR solves the following three problems as far as I've researched.

The Preferences modal content does not display at all in the mobile viewport

Reported by #57494. The Preferences modal component uses the NavigatorProvider when it's a mobile viewport.

Global style sidebar layout

• Go to the Site Editor and go to Global Styles > Blocks
• Fixes unintended changes to sidebar width and scrollbar edge position

trunk	this PR

Content of one story is not displayed in Storybook

When you access the URL below, nothing should be displayed.

https://wordpress.github.io/gutenberg/?path=/story/components-experimental-navigator--skip-focus

Why?

contain: strict is equivalent to contain: size layout paint style. According to MDN, if a value contains size, it appears to have a size of zero if no size is explicitly specified for that element.

If you turn on contain: size you need to also specify the size of the element you have applied this to using contain-intrinsic-size (or the equivalent longhand properties). It will end up being zero-sized in most cases, if you don't manually give it a size.

It's not a problem if the element has an explicit height or flex-glow:1 etc., but if not, problems like those reported by #57494 will occur.

How?

We can probably fix the problem by leaving it as contain: strict and adjusting the CSS that is causing the problem. However, I think we should change from strict to content to avoid such issues at the component level, to avoid impacting consumers and forcing them to set an explicit height. There may be a performance drop compared to strict, but I personally think this is acceptable.

Testing Instructions

Please confirm that the three issues mentioned at the beginning of the explanation have been resolved.

[ciampo]

Thank you for working on the fix and for the detailed PR description 🚀