feat(VCard): conditional card loader display if slot or loading prop

[paul-thebaud]

Description

This PR proposal is to conditionaly display the card loader on VCard component : it is now only displayed when the loading prop value is different than undefined or the loader slot is defined to any value.

Motivation and Context

The loader is currently rendered in the page with a tricky method (height of 0). This creates accessibility problems and generate useless component rendering when the loader isn't used.

How Has This Been Tested?

None for now. I can add test but I will need some guidances please.

Types of changes

• [ ] 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)
• [x] Improvement/refactoring (non-breaking change that doesn't add any features but makes things better)

Checklist:

• [x] The PR title is no longer than 64 characters.
• [x] The PR is submitted to the correct branch (master for bug fixes and documentation updates, dev for new features and backwards compatible changes and next for non-backwards compatible changes).
• [x] My code follows the code style of this project.
• [ ] I've added relevant changes to the documentation (applies to new features and breaking changes in core library)