[-Wunsafe-buffer-usage] Emit fixits for array decayed to pointer (#80347)

Covers cases where DeclRefExpr referring to a const-size array decays to a
pointer and is used "as a pointer" (e. g. passed to a pointer type
parameter).

Since std::array<T, N> doesn't implicitly convert to pointer to its element
type T* the cast needs to be done explicitly as part of the fixit
when we retrofit std::array to code that previously worked with constant
size array. std::array::data() method is used for the explicit
cast.

In terms of the fixit machine this covers the UPC(DRE) case for Array fixit strategy.
The emitted fixit inserts call to std::array::data() method similarly to
analogous fixit for Span strategy.