Fluid typography: add min and max viewport width configurable options

[ramonopoly]

Let's add configurable min and max viewport width values to the typography.fluid theme.json schema, to allow theme developers to configure their own default min and max viewport widths for calculating fluid font sizes.

"What do the min and max viewport widths do?" you ask? Good question.

They define the boundaries, in terms of viewport widths, at which font size clamp values will stop being "fluid". For example, consider the following theme.json settings

Gutenberg PR has been merged: ​https://github.com/WordPress/gutenberg/pull/53081

As well as the core PHP changes, a NPM package update will be required to complete this task.

Backporting PHP changes from:

• ​https://github.com/WordPress/gutenberg/pull/53081

This PR adds configurable min and max viewport width values to the typography.fluid theme.json schema, to allow theme developers to configure their own default min and max viewport widths for calculating fluid font sizes.

The min and max viewport widths the boundaries, in terms of viewport widths, at which font size clamp values will stop being "fluid".

See ​https://github.com/WordPress/gutenberg/pull/53081 for testing instructions.

Note that this PR will only affect the frontend.

A package update is required for the editor to reflect the changes.

Trac ticket: https://core.trac.wordpress.org/ticket/59048

Backporting PHP changes from:

• ​https://github.com/WordPress/gutenberg/pull/53081

This PR adds configurable min and max viewport width values to the typography.fluid theme.json schema, to allow theme developers to configure their own default min and max viewport widths for calculating fluid font sizes.

The min and max viewport widths the boundaries, in terms of viewport widths, at which font size clamp values will stop being "fluid".

See ​https://github.com/WordPress/gutenberg/pull/53081 for testing instructions.

Note that this PR will only affect the frontend.

A package update is required for the editor to reflect the changes.

Trac ticket: https://core.trac.wordpress.org/ticket/59048

[isabel_brison]

In 56535:

Editor: add configurable viewport sizes for fluid typography.

Adds options to configure min and max viewport sizes for fluid typography in theme.json settings.

Props ramonopoly.
Fixes #59048.

Committed in r56535.