siw: Support exclude filter of single files e.g. './file.ext'

[alvsan09]

Bug Description:

When searching in workspace trying to filter out a single file is not currently possible,
as it can be seen in the pictures below, specifying a single file by relative address does make any impact,
and trying to specify the file name removes all files with than name, so leaving no option for the user to
exclude matches coming from a specific file.

See related Issue: #8469

Steps to Reproduce:

From the search view:

1. Input a known pattern present in multiple files
2. Use the 'files to exclude' text box to enter the relative path to one file producing matches, see image below as an example
3. See that no matches are removed

Additional Information

The solution is dependent of: #9307

• Operating System: Linux (although the issue is independent of the OS)
• Theia Version: v1.12.0