Add an option to disable building SelfTest with meson

[Ali-Amir]

Description
Today, there is an option BUILD_TESTING to disable building SelfTest with cmake, however that is not available for meson. The proposal is to add a meson option to building tests directory in Catch2/meson.build:

if get_option('tests')
  subdir('tests')
endif

And add an options file Catch2/meson_options.txt:

option('tests', type: 'boolean', value: true, description: 'Build the unit tests')

Additional context
We're using catch2 as a wrapdb subproject in meson. This allows us to build our code on different platforms without having to install dependencies manually. Since catch2 always includes SelfTest in its meson.build, we end up running SelfTest along with our unit tests when we run meson test.

[aholster]

@Ali-Amir You should probably propose this at the Meson repository instead, as they maintain the Wrapdb meson build definitions

[Ali-Amir]

@aholster it looks like the change needs to happen in this repository, doesn't it? In order for Wrapdb to pass these options to Catch2, Catch2 build file needs to support them. Please, let me know if I'm missing something.

[horenmar]

I'll merge a PR that adds this.

[Ali-Amir]

Thanks @horenmar. I created a PR for this: #2693.