ci(tests): add test framework

[ReenigneArcher]

Description

This PR adds a test framework and initial unit tests. Replaces #1323.

Tests are run in all CI builds (except flatpak right now as it's failing to build). Doc Tests are skipped on macOS (due to dependencies relying on homebrew boost), but are enabled in the Macports build.

Other updates:

• Doxyfile was updated to latest version
• License corrected in ArchLinux PKGBUILD spec
• Moved flatpak shared modules to a submodule

Todo:

• Fix flatpak build
• Determine how to handle cmake components
• Add coverage report
• Upload coverage to codecov
• Disable optimizations for test executable
• Make homebrew spec run tests
• Generate coverage report for Portfile or Homebrew build, and upload
• Add fixtures for nvidia, amd, etc... automatically skipping tests that rely on those fixtures when conditions are incorrect (depends on refactor(video): move encoder declarations to header #2185)
• Add more initial tests

Screenshot

Issues Fixed or Closed

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Dependency update (updates to dependencies)
• Documentation update (changes to documentation)
• Repository update (changes to repository files, e.g. .github/...)

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added or updated the in code docstring/documentation-blocks for new or existing methods/components

Branch Updates

LizardByte requires that branches be up-to-date before merging. This means that after any PR is merged, this branch
must be updated before it can be merged. You must also
Allow edits from maintainers.

• I want maintainers to keep my branch updated