feat: Remove mutable props concept

[maxpatiiuk]

Prerequisites

• I have read the Contributing Guidelines.
• I agree to follow the Code of Conduct.
• I have searched for existing issues that already include this feature request, without success.

Describe the Feature Request

As it stands now, prop being mutable doesn't do anything other than suppress a warning about modifying a prop.
Is there a reason that warning was put in?
This seems like a needless behavior that only worsens DX, and makes testing components harder.

Describe the Use Case

• Do two-way sync of props with external store
• Modify props in tests
• Reset prop values on hot-module-replacement

Describe Preferred Solution

Remove the useless warning

Describe Alternatives

OR deprecate the concept of non-mutable props
OR add a stencil config option to make all props mutable

Related Code

No response

Additional Information

Related to #3490