Describe the bug
Multiselect field does not filter and its dropdown is clipped.

Galaxy Version and/or server at which you observed the bug
Current dev

Browser and Operating System
Operating System: macOS
Browser: Chrome

To Reproduce
Steps to reproduce the behavior:

1. Click on Edit icon of a History Dataset
2. Navigate to Edit Dataset Attributes
3. Attempt to search for a certain datatype in the select field.
4. Also notice that the select field is cut off

Screenshots