Add Twitter & Linkedin logotypes to icon package

We can't use altered logotypes from Phosphor Icons. Add components with real logotypes (look at how SpinnerIcon is included as a custom icon). Also make sure to follow color rules for said logotypes.

SVGs need to be optimized, minified & cleaned "uncolored" (currentcolor) + "unsized" (remove width & height).

Guidelines for Twitter logo (blue + white) https://about.twitter.com/content/dam/about-twitter/en/brand-toolkit/downloads/twitter-external-brand-guidelines-01272021.pdf
https://upload.wikimedia.org/wikipedia/commons/6/6f/Logo_of_Twitter.svg

Guidelines for Linkedin logo (blue + white + black) https://brand.linkedin.com/policies
https://upload.wikimedia.org/wikipedia/commons/8/81/LinkedIn_icon.svg