docs: add Icons rendering section

[julien-deramond]

Description

This PR adds a section explaining how icons are built/rendered within a square and with a safe zone.

Motivation & Context

In projects, we are often wondering whether this safe zone is normal or not. Some designers in the projects remove them, some keep them. The purpose here is to fix this rule in our documentation.

Types of change

• Enhancement (non-breaking change which adds functionality)

Live previews

• https://deploy-preview-2217--boosted.netlify.app/docs/5.3/extend/icons/#icons-rendering

Checklist

Contribution

• I have read the contributing guidelines

Documentation

• My change introduces changes to the documentation and/or I have updated the documentation accordingly

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[hannahiss]

Maybe we could add an icon less "rounded"? Maybe tick and/or delete? The size difference would be more obvious...

[hannahiss]

I think it's great to have theses explanations... Some comments:

• Maybe we could add an icon less "rounded"? Maybe tick and/or buy? The size difference will be more obvious...
• Icons rendering could be a level 2 title directly after the introduction of the page regarding PR Docs: enhance doc for Solaris icons #2075
• I would add a little bit more explanations eg:
  Icons are created in a square layout to maintain consistency. This square contains a safety zone that allows the icons to be used in different sizes and contexts and still be aligned as the designers wish. The size of the icons includes this safety zone.

[julien-deramond]

Thanks for your comment @hannahiss! It's been taken into account in d362d15.

[hannahiss]

there exists => there is ?
2 times ensure/ensuring => there is a designated safety zone to ensure that icons can be used in various sizes and contexts while keeping alignment as intended by the designers ?