ui5-shellbar: logos wider than 3rem are being compressed

[Lukas742]

Describe the bug
If an image wider than 3rem is added to the logo slot of the ui5-shellbar, it is compressed. It's now necessary to overwrite the max-width of the <img> (which is 3rem) to display the image at the correct scale. In rc7 this was not required.

To reproduce
Steps to reproduce the behavior:

1. Implement a ui5-shellbar component
2. Add the logo slot with an image wider than high (should be wider than 3rem inside the shellbar)

Isolated example
1.0.0-rc.8:
https://codesandbox.io/s/ui5-webcomponents-cs3zz?file=/index.html:226-307

1.0.0-rc.7:
https://codesandbox.io/s/ui5-webcomponents-w4k2w?file=/index.html

Expected behavior
Either it should be mentioned in the documentation, that max-width has to be overwritten to display the logo with correct dimension, or the logo should behave like it did with the rc7 version, just with an image tag.

Screenshots

Context

• UI5 Web Components version: 1.0.0-rc.8: