[roll] Roll fuchsia [fidlc] Allow implicit conversions for diagnostic arguments

This CL makes error reporting more ergonomic by allowing implicit
conversions for diagnostic arguments. It also makes it more efficient by
ensuring arguments are always passed by const reference.

Without implicit conversions, you had to explicitly cast:

    Foo*        -> const Foo*
    Derived*    -> Base*
    std::string -> std::string_view
    const char* -> std::string_view
    0           -> size_t(0)

Because of this, error arguments used inconsistent types to minimize
casting at call sites. Refactoring code led to churn in these types in
diagnostics.h. These problems are now fixed, and unnecessary casts have
been removed. See the comment in tools/fidl/fidlc/include/fidl/utils.h
for an explanation of how this works.

An alternative would be to sidestep the deduction issue by providing the
DiagnosticDef and its argument in different calls. For example, we could
have an operator() on ErrorDef/WarningDef that takes the arguments.
However, this isn't obviously better and would cause a huge diff.

Test: fx test fidl-compiler
Original-Fixed: 90046
Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/615624
Original-Revision: b467e6a4053654a5f43a30ae12afcec846b66ee8
GitOrigin-RevId: 2944e0ab0ceb229411c849cc6625195ddb18f171
Change-Id: I61a1a22d005aa7e71247694f394a4af48d2dbff6