Mechanics CTest updates

The 1e-16 is not needed because the Newton solver
tolerance is only 1e-8.

Tighter tolerance for displacement and slightly relaxed for sigma.

The relative tolerances are not used.

Maybe this went missing on migration to declarative pipeline...

[BL] Use implementation specific [[noreturn]].

Unfortunately the Visual Studio 2015 does not support
the platform independent style for the function attributes.
Although it is a c++11 standard.

Disable PCH on macOS

See https://github.com/sakra/cotire/issues/139.

Added a missed parameter documentation and ran clang-tidy for some files

Heterogeneous docu benchmarks

LIE/HM preparations

After removing the 3rd component from the Darcy velocity
and testing for a tight fit.

Alse remove unused computation from computeSecondaryVariableConcreteWithVector().

for consistency.

[web] Fixed links

- Introduced data-url shortcode
- Fixed test data links
- Markdownify text in shortcodes (e.g. image captions, data-url)