[BUG] [mgt-people-picker] search is enabled even if a user is selected and mode is single

[s-KaiNet]

Describe the bug
When default-selected-user-ids is set and selection-mode="single", you are able to put a cursor in the control input and try to further filter, but the component shouldn't allow it.

To Reproduce
Steps to reproduce the behavior:

1. Create a regular <mgt-people-picker> component.
2. Set default-selected-user-ids to a single user id, set selection-mode="single"
3. After the component is loaded, put a cursor next to the preselected user and try to type anything. You will be able to enter a text, but it should be prohibited, since maximum users already added.

Expected behavior
When selection mode is single and default users (or groups) are already set, you shouldn't be able to type anything in the control's input field.

Screenshots

2024-02-21_11-59-58.mp4

Additional info
It could be related to this comment - looks like the issue is fixed only for a situation, when user is selected manually from single-moded control, but not fixed when the use is preselected with default-selected-user-ids.

Environment (please complete the following information):

• OS: any
• Browser: edge, chrome
• Framework: none
• Context: any
• Version: 4.0.1
• Provider: any

[gavinbarron]

Thanks for the high quality bug report @s-KaiNet
Looks like we failed to account for the default selection case.