Add setStyle utility

[cristiano-belloni]

Description

This PR adds the setStyle utility, which adds a CSS rule in the head of the current document.

Motivation and Context

This is factored out from the grid and added here as a general-purpose utility. setStyle is particularly useful when we have a lot of heterogeneous elements (e.g. grid cells) and we want to change the appearance of them all without selecting them and changing each of them.
One practical example I'm using this for is highlighting the grid columns in a "cross-hairs" fashion on hover: it can't be done via CSS and doing that the traditional way would involve selecting all the cells in the column on mouseEnter and mouseLeave + adding or removing a class for each of them.
setStyle does the same job by efficiently changing only its dedicated <style> element.

How Was This Tested?

Manually, on the examples sandbox.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My change follows the style of this project
• My change requires a change to the documentation
• I have updated the documentation accordingly
• I have read the contribution guidelines
• I have added tests to cover my changes
• All new and existing tests passed

[gabrielmontagne]

Good stuff. Thanks. I think it's good to have it out here.
Will create an issue on the grid to use this instead of its own internal organelle.

[gabrielmontagne]

v3.5.0 with this change has been published to npm : ) thanks all.