AK: Forbid `from_utf8` and `from_deprecated_{...}` with unintended types

Calling `from_utf8` with a DeprecatedString will hide the fact that we
have a DeprecatedString, while using `from_deprecated_string` with a
StringView will silently and needlessly allocate a DeprecatedString,
so let's forbid that.

AK/FlyString.h

@@ -21,6 +21,10 @@ public:
     ~FlyString();
 
     static ErrorOr<FlyString> from_utf8(StringView);
+    template<typename T>
+    requires(IsOneOf<RemoveCVReference<T>, DeprecatedString, DeprecatedFlyString>)
+    static ErrorOr<String> from_utf8(T&&) = delete;
+
     FlyString(String const&);
     FlyString& operator=(String const&);
 
@@ -54,6 +58,9 @@ public:
     // FIXME: Remove these once all code has been ported to FlyString
     [[nodiscard]] DeprecatedFlyString to_deprecated_fly_string() const;
     static ErrorOr<FlyString> from_deprecated_fly_string(DeprecatedFlyString const&);
+    template<typename T>
+    requires(IsSame<RemoveCVReference<T>, StringView>)
+    static ErrorOr<String> from_deprecated_fly_string(T&&) = delete;
 
     // Compare this FlyString against another string with ASCII caseless matching.
     [[nodiscard]] bool equals_ignoring_ascii_case(FlyString const&) const;

AK/String.h

@@ -64,6 +64,9 @@ public:
 
     // Creates a new String from a sequence of UTF-8 encoded code points.
     static ErrorOr<String> from_utf8(StringView);
+    template<typename T>
+    requires(IsOneOf<RemoveCVReference<T>, DeprecatedString, DeprecatedFlyString>)
+    static ErrorOr<String> from_utf8(T&&) = delete;
 
     // Creates a new String by reading byte_count bytes from a UTF-8 encoded Stream.
     static ErrorOr<String> from_stream(Stream&, size_t byte_count);
@@ -225,6 +228,9 @@ public:
     // FIXME: Remove these once all code has been ported to String
     [[nodiscard]] DeprecatedString to_deprecated_string() const;
     static ErrorOr<String> from_deprecated_string(DeprecatedString const&);
+    template<typename T>
+    requires(IsSame<RemoveCVReference<T>, StringView>)
+    static ErrorOr<String> from_deprecated_string(T&&) = delete;
 
 private:
     // NOTE: If the least significant bit of the pointer is set, this is a short string.

Userland/Libraries/LibCore/System.cpp

@@ -1047,7 +1047,7 @@ ErrorOr<String> mkdtemp(Span<char> pattern)
         return Error::from_errno(errno);
     }
 
-    return String::from_utf8({ path, strlen(path) });
+    return String::from_utf8(StringView { path, strlen(path) });
 }
 
 ErrorOr<void> rename(StringView old_path, StringView new_path)