Most of these will not matter in practice due to C++14 imposing
significant limitations on what else we can make constexpr, and we cannot
have references outliving the constexpr context either way.

This PR introduces a new `TEST_CASE` macro called `TEST_CASE_PERSISTENT_FIXTURE`. `TEST_CASE_PERSISTENT_FIXTURE` offers the same functionality as `TEST_CASE_METHOD` except for one difference. The object on which the test method is invoked is only created once for all invocations of the test case. The object is created just after the `testCaseStarting` event is broadcast and the object is destroyed just before the `testCaseEnding` event is broadcast.

The main motivation for this new functionality is to allow `TEST_CASE`s to do expensive setup and teardown once per `TEST_CASE`, without having to resort to abusing event listeners or static function variables with manual initialization.


Implements #1602

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

When using the public headers of catch2 in another project
that uses clang-tidy with some checks enabled, then some
warnings in catch2's headers are also reported.

This fixes a bunch of bugprone-macro-parentheses warnings.

See: https://clang.llvm.org/extra/clang-tidy/checks/bugprone/macro-parentheses.html

Closes #2681