Enforce readonly properties immutability

[galargh]

This issue captures the 2nd part of the work identified in the following conversation https://nomicfoundation.slack.com/?redir=%2Farchives%2FC03P6B72ZHU%2Fp1732272638933179%3Fname%3DC03P6B72ZHU%26perma%3D1732272638933179. I think it might make the most sense to add it to the backlog for now.

In the following snippet:

interface Foo {
	readonly bar: Bar;
}

the property bar is readonly, but it is not immutable. To enforce immutability on the type level, it would have to be wrapped in a Readonly utility type like so:

interface Foo {
	readonly bar: Readonly<Bar>;
}

The latter is most often the desired behaviour as showcase by #5971, for example.

I propose enforcing that all non-primitive types found next to the class/object/interface readonly properties are wrapped in the Readonly utility type.

An example of one possible implementation of this rule can be found at #6006