Added casesApp feature icon

[cchaos]

As provided by @JessSmithSup; cc @cnasikas

Also, I edited the SVGO plugin set to exclude removeUselessStrokeAndFill because sometimes fillRule is absolutely necessary. Otherwise the icon was rendering without the hole in the magnifier:

Checklist

• Checked in both light and dark modes
• [ ] Checked in mobile
• Checked in Chrome, Safari, Edge, and Firefox
• [ ] Props have proper autodocs and playground toggles
• Added documentation
• [ ] Checked Code Sandbox works for any docs examples
• Added or updated jest and cypress tests
• [ ] Checked for breaking changes and labeled appropriately
• [ ] Checked for accessibility including keyboard-only and screenreader modes
• Updated the Figma library counterpart
• A changelog entry exists and is marked appropriately

[kibanamachine]

Preview documentation changes for this PR: https://eui.elastic.co/pr_5779/

[cee-chen]

Not sure if it matters, but the removeUselessStrokeAndFill change worried me slightly with the # of snapshot diffs. Should we modify the originating SVGs to remove their fillRule attributes so that their end snapshots don't change? (since they weren't present previously, presumably we don't need them).

I'm probably overthinking how much fill-rule even does though, so TBH I'm fine either way :)

[cchaos]

Yeah, sorry I meant to mention, that I double checked those icons and they're fine with and without that setting. There was technically only 11 icons that changed for that setting, so I didn't think it a big deal to have to go through all the SVG's.

The one thing that got me though, is that without that setting some icons did still keep that fill-rule in their .tsx version. I just don't know when it decides to keep it or remove it, and no matter the amount of changing the .svg would keep that setting during the compiling.

It's not a harmful setting, just sometimes unnecessary.

[cee-chen]

Thanks for that QA!! Agreed that's super weird and the rule seems a bit buggy/inconsistent/not super well documented. I'm good with turning it off!