[BUGFIX] Set fixed widths for extension manager ui elements

The search field has now an own class to apply css before
the wrapper gets rendered. The extension list table columns
have now explicit widths. This ensures the view is not slightly
changing after initial JavaScript operations.

Resolves: #91732
Releases: master, 10.4
Change-Id: Ic9ce327cfa6b5e415974792ee33896540e5a3de6
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/64992


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Riccardo De Contardi <erredeco@gmail.com>
Tested-by: Daniel Goerz <daniel.goerz@posteo.de>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Daniel Goerz <daniel.goerz@posteo.de>