Fluid typography: allow individual preset overrides

[ramonopoly]

Individual font sizes may opt out of fluid typography if it is turned on globally.

Individual font size presets should also be able to opt in to fluid typography if it is not turned on globally.

See the original Gutenberg issue:

​https://github.com/WordPress/gutenberg/issues/64766

This PR syncs the following Gutenberg PR:

• ​https://github.com/WordPress/gutenberg/pull/64790

## What?

This PR allows individual font preset overrides.

So, if fluid typography is disabled or not active but an individual font preset does enable it, calculate the clamp value for that individual preset.

## Why?

Individual font sizes may opt out of fluid typography if it is turned on globally.

This PR does the opposite: individual font size presets can opt in to fluid typography if it is not turned on globally.

## How?

Check if fluid settings on individual font size presets are present.

## Testing Instructions

1. In a theme's theme.json, enable fluid typography for some individual font size presets by adding "fluid": true to the preset object. See the below example theme.json.
2. Make sure fluid typography is not enabled globally in the general "settings.typography" settings.
3. In the editor, apply some of your presets.
4. The presets that have fluid settings should have fluid font sizes in the editor and the frontend.
5. The presets that have no fluid settings should behave as static font sizes.

[!NOTE]
This only affects the frontend site, not the editor.

<details>

<summary>Here is some test theme.json</summary>

{
        "$schema": "https://schemas.wp.org/trunk/theme.json",
        "version": 3,
        "settings": {
                "typography": {
                        "fontSizes": [
                                {
                                        "name": "Big bill",
                                        "size": "59px",
                                        "slug": "big-bill"
                                },
                                {
                                        "name": "Medium Matt",
                                        "size": "30px",
                                        "slug": "med-matt",
                                        "fluid": true
                                },
                                {
                                        "name": "Small Ted",
                                        "size": "1rem",
                                        "slug": "small-ted",
                                        "fluid": {
                                                "max": "60px",
                                                "min": "30px"
                                        }
                                }
                        ]
                }
        }
}

</details>

Trac ticket: https://core.trac.wordpress.org/ticket/61932

Thanks for testing! I'll update those small things.

I'm assuming it's just a copy pasta from the Gutenberg PR.

You assume correctly 😄 I'll update.

[ramonopoly]

In 58950:

Fluid typography: allow individual preset overrides

In theme.json, individual font sizes may opt out of fluid typography if it is turned on globally.

This commit ensures that individual font size presets can also opt in to fluid typography if it is not turned on globally.

Props aaronrobertshaw, mmaattiiaass, ramonopoly, wildworks.

Fixes #61932.

Committed in r58950 / ​https://github.com/WordPress/wordpress-develop/commit/e2c4f64c1e7d56d8562fd2600bf252f6554ce1c2