Allow setting the default icon set

[davidjamesb]

Hey @mathewtaylor.

I previously contributed the Font Awesome icon package which we are using across our application.

We're in a scenario now where we have a mix of icons - with our custom components using Font Awesome and the default out of the box Blueprint components using Lucide.

It's not a huge deal, but it does mean we have inconsistencies in our design. It would be great if we had an option to override the default icons used across Blueprint and wanted to get your thoughts before I take a stab at it myself.

I can see two possible approaches:

1. Provide a global configuration object that can set the icon set application wide and modify the components to switch out the icon based on the chosen icon set. We would need to ensure each available icon set has a like-for-like icon.

This global configuration idea has also been raised in #488.

2. Expose RenderFragments (e.g IconContent) for all current components that have icons out of the box. Stick with Lucide for the default but give the user an escape hatch to be able to override each one.

Neither approaches seem trivial but I know we already expose IconContent in some components so maybe that approach is preferred.

Any other ways you would recommend that we could extend Blueprint so we can align icons across our design?

Thanks.