Deprecate `@Type` and provide better `@Nested`

[temeddix]

Description

The @Type decorator had 2 problems:

• Its name makes itself look like a general type decorator for any variables. However, it's actually only for 'nested class properties'
• Its syntax was unnecessarily dirty: @Type(() => MyClass))

This PR introduces a new @Nested decorator, deprecating @Type, with better JSDoc comments and usage syntax.

Before:

class Photo {
  id!: number;
  filename!: string;
  depth!: number;
}

class Pages {
  table!: number;
  contents!: number;
}

class Album {
  id!: number;
  name!: string;
  @Type(() => Photo)
  photos!: Array<Photo>;
  @Type(() => Pages)
  pages!: Pages;
}

After:

class Photo {
  id!: number;
  filename!: string;
  depth!: number;
}

class Pages {
  table!: number;
  contents!: number;
}

class Album {
  id!: number;
  name!: string;
  @Nested(Photo)
  photos!: Array<Photo>;
  @Nested(Pages)
  pages!: Pages;
}

Documentations are all properly updated. Users using VSCode will receive deprecation warning because @Type is now marked with @deprecated, so that they can gradually transition later on.

Checklist

• [x] the pull request title describes what this PR does (not a vague title like Update index.md)
• [x] the pull request targets the default branch of the repository (develop)
• [x] the code follows the established code style of the repository
  • npm run prettier:check passes
  • npm run lint:check passes
• [x] tests are added for the changes I made (if any source code was modified)
• [x] documentation added or updated
• [x] I have run the project locally and verified that there are no errors

Fixes

fixes #[issue number], fixes #[issue number]

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