[ADT] Deprecate Optional::map

[kazu]

Summary

This patch deprecates Optional::map in favor of Optional::transform
for consistency with std::optional::transform in C++23.

Note that I've migrated all known users of Optional::map.

[dblaikie]

Sounds good!

llvm/include/llvm/ADT/Optional.h

public:
   /// Apply a function to the value if present; otherwise return None.
   template <class Function>
   auto transform(const Function &F) const & -> Optional<decltype(F(value()))> {
     if (*this)
       return F(value());
     return None;
   }
   template <class Function>
+  LLVM_DEPRECATED("Use transform instead.", "transform")
   auto map(const Function &F) const & -> Optional<decltype(F(value()))> {
     if (*this)
       return F(value());
     return None;
   }
 
   T &&value() && { return std::move(Storage.value()); }
   LLVM_DEPRECATED("Use value instead.", "value") T &&getValue() && {
public:
   template <class Function>
   auto transform(
       const Function &F) && -> Optional<decltype(F(std::move(*this).value()))> {
     if (*this)
       return F(std::move(*this).value());
     return None;
   }
   template <class Function>
+  LLVM_DEPRECATED("Use transform instead.", "transform")
   auto map(const Function &F)
       && -> Optional<decltype(F(std::move(*this).value()))> {
     if (*this)
       return F(std::move(*this).value());
     return None;
   }
 };