🐛(lib-video) fix display issues with picture shared ressource in live

[AntoLC]

Purpose

(live) glitch d'affichage du partage de documents en mode fenêtré sur navigateur.

https://trello.com/1/cards/654b8ab615e123d2213a9c9a/attachments/655347173d05e4332536b0e1/download/Partage_de_document_-_responsiveness.webm

https://trello.com/1/cards/654b8ab615e123d2213a9c9a/attachments/65534793bf00d478bfc1589f/download/Partage_de_document_-_responsiveness_02.webm

Fixed

• [x] icons could sometime be duplicated between layers
• [x] positioning was not everytime correct, with a icon on the top left corner of the screen
• [x] icons too big
• [x] improve spacing in title box live

Observation

The width of the vignette is limited here: https://github.com/openfun/marsha/blob/d55f4d5e95c075291f2a27e775f8a65f363b7f36/src/frontend/packages/lib_video/src/conf/pictureInPicture.ts#L3

It could have been nice to increase to 0.8, but we get a responsive problem with the height, it asks a not so small refacto to be able to make it works correctly.