feat(`@vtmn/svelte`): add focus event support for Svelte version of `VtmnTextInput`

[BasileRaiwet]

Changes description

Adding support of focus event on the VtmnTextInput for svelte. This change has been archived by adding on:focus directive to the input and textarea elements.

Context

We are currently using this component in Belgium (NFS) and we need to handle the focus event. Actually we need to do it by manipulating the DOM and adding event listener manually, which is not great In terms of readability and maintainability.

Checklist

• [x] Make sure you are requesting to pull a topic/feature/bugfix branch. Please, don't request directly from your main!
• [x] Check commits & PR names matches our requested structure. It must follow the https://www.conventionalcommits.org pattern.
• [x] Check your code additions will fail neither code linting checks.
• [x] I have reviewed the submitted code.
• [x] I have tested on related showcases.

Does this introduce a breaking change?

• No

[CLAassistant]

All committers have signed the CLA.

[BasileRaiwet]

@Tlahey @thibault-mahe When can we expect this PR to be merged / deployed ? Just to get an idea, because it could really help us in a current development

[lauthieb]

Hi @BasileRaiwet, thanks for this PR! I just came back from vacation. For me that's ok, I approved. I just wait for the CI and when all it's ok, I merge it :)