[libc] Move CharacterConverter template specialization to cpp file (#152405)

Fixes build errors caused by #152204

Author: uzairnawaz

libc/src/__support/wchar/character_converter.cpp

@@ -164,5 +164,13 @@ ErrorOr<char8_t> CharacterConverter::pop_utf8() {
   return static_cast<char8_t>(output);
 }
 
+template <> ErrorOr<char8_t> CharacterConverter::pop() { return pop_utf8(); }
+template <> ErrorOr<char32_t> CharacterConverter::pop() { return pop_utf32(); }
+
+template <> size_t CharacterConverter::sizeAs<char8_t>() {
+  return state->total_bytes;
+}
+template <> size_t CharacterConverter::sizeAs<char32_t>() { return 1; }
+
 } // namespace internal
 } // namespace LIBC_NAMESPACE_DECL

libc/src/__support/wchar/character_converter.h

@@ -33,17 +33,13 @@ class CharacterConverter {
   bool isValidState();
 
   template <typename CharType> size_t sizeAs();
-  template <> size_t sizeAs<char8_t>() { return state->total_bytes; }
-  template <> size_t sizeAs<char32_t>() { return 1; }
 
   int push(char8_t utf8_byte);
   int push(char32_t utf32);
 
   ErrorOr<char8_t> pop_utf8();
   ErrorOr<char32_t> pop_utf32();
   template <typename CharType> ErrorOr<CharType> pop();
-  template <> ErrorOr<char8_t> pop() { return pop_utf8(); }
-  template <> ErrorOr<char32_t> pop() { return pop_utf32(); }
 };
 
 } // namespace internal