[Issue 14919] utf/unicode should only be validated once

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=14919

--- Comment #3 from Martin Nowak <code at dawg.eu> ---
The transition could be done in the following order over several releases:

1. `deprecate("use UTFError instead") UTFException` and add `alias UTFError =
UTFException`, so UTFError remains an Exception
   use UTFError in all validations

2. make UTFError an Error
   change all text reading functions (e.g. byLine) to eager validations

3. replace validations and UTFError with asserts

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