Doc: QLatin1StringView documentation misses string literals namespace

QLatin1StringView documentation assumes knowledge of string literals
namespace. This commit adds a 'using' statement to the code samplles
that use string literals.

Fixes: QTBUG-135945
Pick-to: 6.8
Change-Id: I17971d343d9dad132394b91d93ac045c2c8d019f
Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
(cherry picked from commit 72becc7c124f27ad1506ed4fc49d9abe1242629b)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/corelib/doc/snippets/code/src_corelib_io_qabstractfileengine.cpp

@@ -1,9 +1,9 @@
 // Copyright (C) 2016 The Qt Company Ltd.
 // SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
 
-using namespace Qt::StringLiterals;
-
 //! [0]
+using namespace Qt::StringLiterals;
+// ...
 class ZipEngineHandler : public QAbstractFileEngineHandler
 {
 public:

src/corelib/doc/snippets/code/src_corelib_mimetype_qmimedatabase.cpp

@@ -12,6 +12,8 @@ if (mime.inherits("text/plain")) {
 //! [0]
 
 //! [1]
+using namespace Qt::StringLiterals;
+// ...
 QStandardPaths::locateAll(QStandardPaths::GenericDataLocation, "mime/packages"_L1,
                           QStandardPaths::LocateDirectory);
 //! [1]

src/corelib/doc/snippets/code/src_corelib_serialization_qcborstream.cpp

@@ -8,6 +8,8 @@ using namespace Qt::StringLiterals;
 //! [0]
 
 //! [1]
+using namespace Qt::StringLiterals;
+// ...
    writer.startMap(4);    // 4 elements in the map
 
    writer.append("label"_L1);
@@ -73,6 +75,8 @@ using namespace Qt::StringLiterals;
 //! [7]
 
 //! [8]
+using namespace Qt::StringLiterals;
+// ...
    writer.append("Hello, World"_L1);
 //! [8]
 

src/corelib/doc/snippets/code/src_corelib_text_qstring.cpp

@@ -1,9 +1,10 @@
 // Copyright (C) 2016 The Qt Company Ltd.
 // SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
 
-using namespace Qt::StringLiterals;
-
 //! [1]
+// Required for using the '_L1' string literal.
+using namespace Qt::StringLiterals;
+// ...
 QString url = "https://www.unicode.org/"_L1;
 //! [1]
 
@@ -35,6 +36,9 @@ str.append("Hello ").append("World");
 //! [4bis]
 
 //! [5]
+// Required for using the '_L1' string literal.
+using namespace Qt::StringLiterals;
+// ...
 if (str == "auto"_L1
         || str == "extern"_L1
         || str == "static"_L1

src/corelib/doc/snippets/hellotrmain.cpp

@@ -1,9 +1,10 @@
 // Copyright (C) 2016 The Qt Company Ltd.
 // SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
 
+//! [0]
+// Required for using the '_L1' string literal.
 using namespace Qt::StringLiterals;
 
-//! [0]
 int main(int argc, char *argv[])
 {
     QApplication app(argc, argv);

src/corelib/doc/snippets/qstring/stringbuilder.cpp

@@ -3,9 +3,11 @@
 
 #include <QString>
 
-using namespace Qt::StringLiterals;
-
 //! [0]
+// Required for using the '_L1' string literal.
+using namespace Qt::StringLiterals;
+// ...
+
     QString foo;
     QString type = "long";