This means that bit-flag-like types with conversion to bool can be
asserted on, like so `REQUIRE(var & Flags::AddNewline)`.

Originally the tests were from #1912, but as it turned out, the issue
was somewhere else. Still, the inputs provided were interesting, so
they are now part of our test suite.

Also removed the iterative checking that seeds 1-100 do not create
the same output, because it used too much runtime.

It did not clear out all of its internal state when switching from
one pattern to another, so when it should've escaped `,`, it took
its position from its position in the original user-provided string,
rather than its position in the current pattern.

Fixes #1905

This is a partial revert of b7b346c3e5603.

The old code caused warnings to fire under MSVC, and Clang <3.8.
I could not find a GCC version where it worked, but I assume that it
did at some point.

This new code causes all of MSVC, GCC, Clang, in current versions,
to emit signed/unsigned comparison warning in test like this:

```cpp
TEST_CASE() {
    int32_t i = -1;
    uint32_t j = 1;
    REQUIRE(i != j);
}
```

Where previously only MSVC would emit the warning.

Fixes #1880

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