FontSizePicker: Show min-max range for fluid font sizes in dropdown.

[karthikeya-io]

What?

Closes #69939

This PR updates the FontSizePickerSelect component to improve how fluid font size presets are displayed in the dropdown. Instead of using the size property as the hint, it now shows values from the fluid property (min and max) when they are available.

Why?

Currently, the FontSizePickerSelect component uses the size property as the hint, even when the fluid property is present. However, the size may not accurately represent the rendered font size for fluid presets, as it is derived from the min–max fluid range.

This change helps reduce confusion by explicitly displaying the fluid font size range in the UI.

How?

Updated the FontSizePickerSelect component to:

• Check for the presence of fluid.min and fluid.max
• Display:
  • Fluid (min – max) when both are defined
  • Fluid (≥ min) when only min is defined
  • Fluid (≤ max) when only max is defined

Testing Instructions

1. Select a block like paragraph or heading
2. Open the Typography → Font Size settings
3. Verify that the dropdown hints use values from the fluid property when its present.
   Note: Update theme.json to have atleast 6 sizes to enable the dropdown selector instead of toggle.

Testing Instructions for Keyboard

Same

Screenshots or screencast

Before	After

[github-actions]

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Co-authored-by: karmatosed <karmatosed@git.wordpress.org>
Co-authored-by: jasmussen <joen@git.wordpress.org>
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[karmatosed]

We could have done with design feedback on the issue before jumping to PR so let's do that first then consider this PR after. For now please don't merge this until a direction is decided.

[jasmussen]

It seems useful enough, and good motivation. My main question here is whether there's a good dropdown component that supports showing these two lines. The component in question, with the dark border, is an older one. I wonder, would you be able to use Menu instead? I think that could thread the needle, and show the ranges as help-text for each item.

[mirka]

Closing this out now since the original issue was closed already. Thanks!