Fix incorrect filter behavior when combining multiple regexp

[Jojo-1000]

Closes #4590

With multiple regexp filters, if an earlier filter matches only part of a path, any other filters were ignored.

Steps to reproduce

• Create/choose folders /a/, /b/ and /a/c/ (names irrelevant)
• Run test-filters command with regexp include filter expression [/(a|b)/] and [/a/c/] and exclude .*

Duplicati.CommandLine.exe test-filters  /a --include="[/(a|b)/]" --include="[/a/c/]" --exclude="[/.*/]"

• See also FilterTests.CombineRegexp

Current behavior

• The regexp expressions are combined to (/(a|b)/)|(/a/c/), which will match the part /a/ of /a/c/. This is detected as a mismatch, so the path is excluded.

New behavior

• The regexp expressions are combined to ^((^(/(a|b)/)$)|(^(/a/c/)$))$ (not ideal in terms of delimiters, but works). This forces the match to the full path /a/c/. The path is included as it should be.