settings_ui: Fix IEEE 754 floating point error when serializing value to JSON

[dongdong867]

Closes #40556

Release Notes:

• settings-ui: Fixed editing fields from settings-ui causing IEEE 754 floating error in settings.json file

Note

Seems like there's another pull request fixing the centered layout in #40661 by normalizing the whole settings.json file when updating it. Not sure which is the better way to handle this issue.

Description

This pull request solves the IEEE 754 floating point error when serializing values from settings-ui into settings.json by creating a two serde_helper to convert the problematic f32 into a formatted two decimal placed f32.

Fields currently exists the IEEE 754 error:

• Appearance → Unnecessary Code Fade
• Editor → Drop Size Target
• Window & Layout → Centered Layout Left/Right Padding
• Window & Layout → Inactive Opacity

How to verify

Unnecessary Code Fade

As Is	To Be
as_is_unnecessary_code.mov	to_be_unnecessary_code.mov

Drop Size Target

As Is	To Be
as_is_drop_size_target.mov	to_be_drop_size_target.mov

Centered Layout Left/Right Padding

As Is	To Be
as_is_centered_layout.mov	to_be_centered_layout.mov

Inactive Opacity

As Is	To Be
as_is_inactive_opacity.mov	to_be_inactive_opacity.mov

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[dongdong867]

@cla-bot check

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[delvin02]

nice work @dongdong867 !

[probably-neb]

Awesome work. Thanks! I've pushed a couple commits, The first one is to make sure all f32 settings get serialized with rounding for consistency and to ensure that regardless of what a user has in their settings, changing it in the settings UI doesn't result in floating error in the settings file. The second is to add some basic tests.

I'm going to merge this once CI passes. Thanks again!

[dongdong867]

Thanks for the follow-up commits and the review!