Doc: Fixed snippet issues in QDoc documentation

QDoc uses .qdoc files as snippets in other .qdoc files. These snippet
.qdoc files are also parsed, which is not the intent. This change
resolves the issue by renaming the files to have a different
extension.

Task-number: QTBUG-31574
Change-Id: I399c8b714478b9c4b8fbe2db53f601e6a1386cea
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>

src/tools/qdoc/doc/qdoc-guide/qtwritingstyle-cpp.qdoc

@@ -41,7 +41,7 @@ Note that the documentation must be in the implementation files such as \c .cpp.
 Class documentation is generated using the \l{class-command}{\\class} command and
 the name of the class as the first argument.
 
-\snippet examples/cpp.qdoc class
+\snippet examples/cpp.qdoc.sample class
 
 \l{Context commands} add information about the class, such as its module or
 which version the class was added.
@@ -79,7 +79,7 @@ Typically, function documentation immediately precedes the implementation of the
 function in the \c .cpp file. For function documentation that is not immediately
 above the implementation, the \l{fn-command}{\\fn} is needed.
 
-\snippet examples/cpp.qdoc function
+\snippet examples/cpp.qdoc.sample function
 
 The function documentation starts with a verb, indicating the operation the
 function performs. This also applies to constructors and destructors.
@@ -102,7 +102,7 @@ The \l{a-command}{\\a} command marks the parameter in the documentation.
 The return type documentation should link to the type documentation or be
 marked with the \l{c-command}{\\c} command in the case of boolean values.
 
-\snippet examples/cpp.qdoc return
+\snippet examples/cpp.qdoc.sample return
 
 \section1 Properties
 
@@ -110,7 +110,7 @@ The property documentation resides immediately above the read function's
 implementation. The \l{topic-commands}{topic command} for properties is
 \l{property-command}{\\property}.
 
-\snippet examples/cpp.qdoc property
+\snippet examples/cpp.qdoc.sample property
 
 Property documentation usually starts with "This property...", but these are
 alternate expressions:
@@ -142,7 +142,7 @@ The \l{topic-commands}{topic command} for signals, notifiers, and slots
 is \l{fn-command}{\\fn}. Signal documentation state when they are triggered
 or emitted.
 
-\snippet examples/cpp.qdoc signals
+\snippet examples/cpp.qdoc.sample signals
 
 Signal documentation typically begin with "This signal is triggered when...".
 Here are alternate styles:
@@ -164,7 +164,7 @@ notifiers together. To refer to a specifc version of a notifier or signal,
 simply refer to the property and mention that there are different versions of
 the notifier.
 
-\snippet examples/cpp.qdoc overloaded notifier
+\snippet examples/cpp.qdoc.sample overloaded notifier
 
 \section1 Enums, Namespaces, and other Types
 
@@ -181,7 +181,7 @@ continues with the type description.
 For enumerations, the \l{value-command}{\\value} command is for listing the
 values. QDoc creates a table of values for the enum.
 
-\snippet examples/cpp.qdoc enums
+\snippet examples/cpp.qdoc.sample enums
 
 */
 

src/tools/qdoc/doc/qdoc-guide/qtwritingstyle-qml.qdoc

@@ -60,7 +60,7 @@ does not exist. The class documentation may be marked as
 
 The \l{qmltype-command}{\\qmltype} command is for QML type documentation.
 
-\snippet examples/qml.qdoc qmltype
+\snippet examples/qml.qdoc.sample qmltype
 
 The \l{instantiates-command}{\\instantiates} accepts the C++ class which
 implements the QML type as the argument. For types implemented in QML, this
@@ -108,7 +108,7 @@ with the \l{qmlsignal-command}{\\qmlsignal} command. Signal documentation
 must include the condition for emitting the signal, mention the corresponding
 signal handler, and document whether the signal accepts a parameter.
 
-\snippet examples/qml.qdoc signals
+\snippet examples/qml.qdoc.sample signals
 
 These are the possible documentation styles for signals:
 \list
@@ -127,7 +127,7 @@ documentation must reside immediately above the function declaration.
 The function documentation starts with a verb, indicating the operation the
 function performs.
 
-\snippet examples/qml.qdoc function
+\snippet examples/qml.qdoc.sample function
 
 Some common verbs for function documentation:
 \list
@@ -153,7 +153,7 @@ QML enumerations are documented as QML properties with the
 \l{qmlproperty-command}{\\qmlproperty} command. The type of the property
 is \c enumeration.
 
-\snippet examples/qml.qdoc enums
+\snippet examples/qml.qdoc.sample enums
 
 The QDoc comment lists the values of the enumeration. If the enumeration is
 implemented in C++, the documentation may link to the corresponding C++