TAP format requires all results to be reported.
Removed extraneous preferences function (handled by parent)
Incorporated fix from 3d9e7db2e0fff8fc2edcf59d24351f3937e3ac62
Simplified total printing

This means that code such as

```cpp
TEST_CASE() {
    SECTION("first") { SUCCEED(); }
    auto _ = GENERATE(1, 2);
    SECTION("second") { SUCCEED(); }
}
```

will run and report 3 assertions, 1 from section "first" and 2
from section "second". This also applies for greater and potentially
more confusing nesting, but fundamentally it is up to the user to
avoid overly complex and confusing nestings, just as with `SECTION`s.

The old behaviour of `GENERATE` as first thing in a `TEST_CASE`,
`GENERATE` not followed by a `SECTION`, etc etc should be unchanged.

Closes #1938

A test runner already has a --durations option to print durations.
However, this isn't entirely satisfactory.

When there are many tests, this produces output spam which makes it hard
to find the test failure output.  Nevertheless, it is helpful to be
informed of tests which are unusually slow.

Therefore, introduce a new option --min-duration that causes all
durations above a certain threshold to be printed.  This allows slow
tests to be visible without mentioning every test.