Diagnostic stores various notes/error messages which might help the user
in debugging. For the most part, the `Diagnostic` when receiving an
error message will copy and own the contents of the string.
However, there is one optimization where given a `const char*`, the
class will assume this is a StringLiteral which is immutable and
lifetime matches that of the entire program. As a result, instead of
copying the message in these cases the class will simply store the
underlying pointer.
This is problematic since `const char*` is not specific enough to always
imply a StringLiteral which can lead to bugs, e.g. if the underlying
pointer is freed before the diagnostic reports.
We solve this problem by choosing a more specific function signature.
While not full-proof, this should cover a lot more cases.
A potentially better alternative is just deleting this special handling
of string literals, but I am unsure of the implications (it does sound
safe to do however with a negligble impact on performance).
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