Fix qdoc warning, \function is not a command

Document the size parameter while at it, and rephrase a bit.

This introduces a new qdoc warning since QtLiteral is a new
namespace without any documentation, but that's for a separate
commit.

Change-Id: I849d5cdde8b64dbbe7e6a526214d422930091cd4
Reviewed-by: Paul Wicking <paul.wicking@qt.io>
Reviewed-by: Andrei Golubev <andrei.golubev@qt.io>
Reviewed-by: Nico Vertriest <nico.vertriest@qt.io>

src/corelib/text/qbytearray.cpp

@@ -4767,17 +4767,19 @@ QByteArray QByteArray::toPercentEncoding(const QByteArray &exclude, const QByteA
 */
 
 /*!
-  \function QtLiterals::operator""_qba(const char *str, size_t size)
+  \fn QtLiterals::operator""_qba(const char *str, size_t size)
 
   \relates QByteArray
   \since 6.2
 
-  Literal operator that creates a QByteArray out of a char string literal \a
-  str. Creating a QByteArray from it is free in this case, and the generated
-  string data is stored in the read-only segment of the compiled object file.
-  Duplicate literals may share the same read-only memory. This functionality is
-  interchangeable with QByteArrayLiteral, but saves typing when many string
-  literals are present in the code.
+  Literal operator that creates a QByteArray out of the first \a size characters
+  in the char string literal \a str.
+
+  The QByteArray is created at compile time, and the generated string data is stored
+  in the read-only segment of the compiled object file. Duplicate literals may share
+  the same read-only memory. This functionality is interchangeable with
+  QByteArrayLiteral, but saves typing when many string literals are present in the
+  code.
 
   The following code creates a QByteArray:
   \code

src/corelib/text/qstring.cpp

@@ -10506,17 +10506,19 @@ QString QString::toHtmlEscaped() const
 */
 
 /*!
-  \function QtLiterals::operator""_qs(const char16_t *str, size_t size)
+  \fn QtLiterals::operator""_qs(const char16_t *str, size_t size)
 
   \relates QString
   \since 6.2
 
-  Literal operator that creates a QString out of a char16_t string literal \a
-  str. Creating a QString from it is free in this case, and the generated string
-  data is stored in the read-only segment of the compiled object file. Duplicate
-  literals may share the same read-only memory. This functionality is
-  interchangeable with QStringLiteral, but saves typing when many string
-  literals are present in the code.
+  Literal operator that creates a QString out of the first \a size characters in
+  the char16_t string literal \a str.
+
+  The QString is created at compile time, and the generated string data is stored
+  in the read-only segment of the compiled object file. Duplicate literals may
+  share the same read-only memory. This functionality is interchangeable with
+  QStringLiteral, but saves typing when many string literals are present in the
+  code.
 
   The following code creates a QString:
   \code