Fixes #2615

Co-authored-by: Garz4 <fancygarz4@gmail.com>
Co-authored-by: Martin Hořeňovský <martin.horenovsky@gmail.com>

* Add new SKIP macro for skipping tests at runtime

This adds a new `SKIP` macro for dynamically skipping tests at runtime.
The "skipped" status of a test case is treated as a first-class citizen,
like "succeeded" or "failed", and is reported with a new color on the
console.

* Don't show "skipped assertions" in console/compact reporters

Also extend skip tests to cover a few more use cases.

* Return exit code 4 if all test cases are skipped

* Use LightGrey for the skip colour

This isn't great, but is better than the deep blue that was borderline
invisible on dark backgrounds. The fix is to redo the colouring
a bit, including introducing light-blue that is actually visible.

* Add support for explicit skips in all reporters

* --allow-running-no-tests also allows all tests to be skipped

* Add docs for SKIP macro, deprecate IEventListener::skipTest

Co-authored-by: Martin Hořeňovský <martin.horenovsky@gmail.com>

Instead of redoing the whole line where path was found, only the
directory part of the path is removed, instead of removing all
of the line before the path starts.

This results in slight change in how junit and sonarqube approvals
come out, and significant change in how TeamCity reporter approvals
come out. This latter difference is the reason for the change,
as now the lines with `testFailed` and `testIgnored` messages
are not completely butchered.

This is needed so that we can use conjunction and other logical
type traits to workaround issue with older GCC versions (8 and
below), when they run into types that have ambiguous constructor
from `0`, see e.g. #2571.

However, using conjunction and friends in the SFINAE constraint
in the template parameter breaks for C++20 and up, due to the new
comparison operator rewriting rules. With C++20, when the compiler
see `a == b`, it also tries `b == a` and collects overload set
for both of these expressions.

In Catch2, this means that e.g. `REQUIRE( 1 == 2 )` would lead
the compiler to check overloads for both `ExprLhs<int> == int`
and `int == ExprLhs<int>`. Since the overload set and SFINAE
constraints assume that `ExprLhs<T>` is always on the left side,
when the compiler tries to resolve the template parameters, all
hell breaks loose and the compilation fails.

By moving the SFINAE constraints to the return type, the compiler
can discard the switched expression without having to resolve
the complex SFINAE constraints, and thus everything works the
way it is supposed to.

Fixes #2571

This reverts commit 291c502f6676b8d304b608f936ec26e3b347054a.

The issue is that it breaks under C++20 for some reason.

Closes #2571

We start at version 2, with version 1 being taken up by the output
from Catch2 v2.