Fixes #2615

They also got slapped with the `[approvals]` tag in the process,
because we have too many approval tests and want less of them,
and these particular tests don't bring much value.

Related to #2090

Not all reporters use a format that supports this, so TeamCity
and Automake reporters still do not report it. The console
reporter now reports it even on successful runs, where before
it only reported the rng seed in the header, which was showed
either for failed run, or for run with `-s`.

CLoses #2065

Removed:
 * NaN normalization
 * INFINITY normalization
 * errno normalization
 * Completely unused duration regex

Tests using these macros should be tagged `[approvals]`
so they are not run as part of approval tests.

Also simplified regex for the test's executable filename,
and hidden some tests relying on nullptr normalization.

This is a simplification of the fix proposed in #2152, with the
critical function split out so that it can be tested directly,
without having to go through the ULP matcher.

Closes #2152

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

Closes #1954

* Successive executions of the same `GENERATE` macro (e.g. because
of a for loop) no longer lead to multiple nested generators.
* The same line can now contain multiple `GENERATE` macros without
issues.

Fixes #1913