ui5-multi-combo-box: Changes width on selection change in some cases

[MarcusNotheis]

Describe the bug
When using the ui5-multi-combobox in a Form-like display mode (label on the left) it changes it's own width when there is an at least one active selection. If no item is selected, the width seems to be fine.

To reproduce
Steps to reproduce the behavior:

1. Open the provided sandbox
2. Deselect the selected item (MCB gets smaller)
3. Select another item (MCB grows again)

Isolated example
https://codesandbox.io/s/ui5-webcomponents-lt2k9?file=/index.html

Expected behavior
I would expect that the MCB does not change its total width.

Screenshots
If applicable, add screenshots to help explain your problem.

Context

• UI5 Web Components version: 1.0.0-rc.7
• OS/Platform: MacOS
• Browser (if relevant): Chrome

Affected components (if known)

• ui5-multi-combobox

Log output / Any errors in the console
Other input components like the select is working fine.

[MarcusNotheis]

Original issue: SAP/ui5-webcomponents-react#564

[MarcusNotheis]

Might be related to #1719 as well?

[MapTo0]

Well ... to be honest I am not sure how we can resolve that issue without setting a fixed width of the combobox.
To me this looks like a flexbox question here is a similar question: https://stackoverflow.com/questions/21406397/width-ignored-on-flexbox-items

Try adding flex-shrink: 0; to the parent (display: flex) container.