[docs] Fix ints that should be qsizetype [src/corelib/text]

For the constructors, replace int with qsizetype. For the incorrect
return type in \fn of length(), drop the return type, the presence of
which violated DRY, stressing the importance of that SOLID principle.

Fixes: QTBUG-103531
Change-Id: Ic7a8e1953333c28a2722fd7f753a0b5af6777395
Reviewed-by: Sona Kurazyan <sona.kurazyan@qt.io>
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
(cherry picked from commit 334c27dad139956135b8687bf695e3cfa0228b9c)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/corelib/text/qanystringview.qdoc

@@ -38,7 +38,7 @@
     When used as an interface type, QAnyStringView allows a single
     function to accept a wide variety of string data sources. One
     function accepting QAnyStringView thus replaces five function
-    overloads (taking QString, \c{(const QChar*, int)},
+    overloads (taking QString, \c{(const QChar*, qsizetype)},
     QUtf8StringView, QLatin1StringView (but see above), and QChar), while
     at the same time enabling even more string data sources to be
     passed to the function, such as \c{u8"Hello World"}, a \c char8_t
@@ -304,7 +304,7 @@
 */
 
 /*!
-    \fn int QAnyStringView::length() const
+    \fn QAnyStringView::length() const
 
     Same as size().
 

src/corelib/text/qbytearrayview.qdoc

@@ -481,7 +481,7 @@
 */
 
 /*!
-    \fn int QByteArrayView::length() const
+    \fn QByteArrayView::length() const
 
     Same as size().
 

src/corelib/text/qstring.cpp

@@ -5610,7 +5610,7 @@ QString QString::fromUtf8(QByteArrayView ba)
     host byte order is assumed.
 
     This function is slow compared to the other Unicode conversions.
-    Use QString(const QChar *, int) or QString(const QChar *) if possible.
+    Use QString(const QChar *, qsizetype) or QString(const QChar *) if possible.
 
     QString makes a deep copy of the Unicode data.
 

src/corelib/text/qstringview.cpp

@@ -32,7 +32,7 @@ QT_BEGIN_NAMESPACE
     When used as an interface type, QStringView allows a single function to accept
     a wide variety of UTF-16 string data sources. One function accepting QStringView
     thus replaces three function overloads (taking QString and
-    \c{(const QChar*, int)}), while at the same time enabling even more string data
+    \c{(const QChar*, qsizetype)}), while at the same time enabling even more string data
     sources to be passed to the function, such as \c{u"Hello World"}, a \c char16_t
     string literal.
 
@@ -481,7 +481,7 @@ QT_BEGIN_NAMESPACE
 */
 
 /*!
-    \fn int QStringView::length() const
+    \fn QStringView::length() const
 
     Same as size().
 

src/corelib/text/qutf8stringview.qdoc

@@ -473,7 +473,7 @@
 */
 
 /*!
-    \fn int QUtf8StringView::length() const
+    \fn QUtf8StringView::length() const
 
     Same as size().