feat(demo): reorganize components and dialog refactor

Description

Closes #152 Closes #153

This commit focuses on restructuring and enhancing the codebase for improved organization and maintainability. The key aspects of this commit include:

Changes made

1. Folder Layout Reorganization.

The demo folder now follows a revised layout structure:

core: Contains common modules and components, such as the spinner, content-link, dialog, spa router, etc.
layout: Houses pages and major layout elements, including the header, example page, search page, etc.

This restructuring aims to make the demo page more intuitive and modular.

2. Refactor `player-dialog` to a web component

The player-dialog has been refactored into a web component. This refactor has led to a cleaner separation of concerns, isolating the dialog's styles from the main page.

3. Player Query Params Routing Logic

The logic responsible for handling the routing of player query parameters has been relocated to the player.js file. This ensures that the routing-related functionality is centralized within the appropriate file.

St.^{:grey_question:}	Category	Percentage	Covered / Total
🟢	Statements	98.39%	489/497
🟢	Branches	93.44%	228/244
🟢	Functions	100%	136/136
🟢	Lines	99.16%	473/477

SRGSSR / pillarbox-web