Doc: Fix QDoc warnings in Extending Qt Creator Manual

Change-Id: I278ae2338427a7d65253d579d0a1ff7d53245c45
Reviewed-by: hjk <hjk@qt.io>

doc/qtcreatordev/src/qtcreator-ui-text.qdoc

@@ -474,7 +474,7 @@
             \li  Mode
             \li  Modes correspond to complete screens of controls, specialized
                  for a task.
-                 \image qtcreator-mode-selector.png {Mode selector}
+                 \image qtcreator-mode-selector.webp {Mode selector}
             \li  You can add a mode for a new type of editor, for example.
                  Use descriptive, but short mode names. They have to fit in the
                  \uicontrol {Mode selector}.

src/libs/utils/filepath.cpp

@@ -304,9 +304,9 @@ bool FilePath::equals(const FilePath &first, const FilePath &second, Qt::CaseSen
 }
 
 /*!
- * Returns true if the two file paths compare equal case-sensitively.
+ * Returns \c true if this file path compares equal to \a other case-sensitively.
  * This is relevant on semi-case sensitive systems like Windows with NTFS.
- * @see QTCREATORBUG-30846
+ * \sa {https://bugreports.qt.io/browse/QTCREATORBUG-30846}{QTCREATORBUG-30846}
  */
 bool FilePath::equalsCaseSensitive(const FilePath &other) const
 {

src/libs/utils/layoutbuilder.cpp

@@ -362,7 +362,7 @@ void Layout::setContentsMargins(int left, int top, int right, int bottom)
 }
 
 /*!
-    Attaches the constructed layout to the provided QWidget \a w.
+    Attaches the constructed layout to the provided QWidget \a widget.
 
     This operation can only be performed once per LayoutBuilder instance.
  */
@@ -373,7 +373,7 @@ void Layout::attachTo(QWidget *widget)
 }
 
 /*!
-    Adds the layout item \a item as sub items.
+    Adds the layout item \a item as a sub item.
  */
 void Layout::addItem(I item)
 {

src/plugins/coreplugin/icore.cpp

@@ -851,7 +851,7 @@ QList<IContext *> ICore::currentContextObjects()
     Returns the widget of the top level IContext of the current context, or \c
     nullptr if there is none.
 
-    \sa currentContextObject()
+    \sa currentContextObjects()
 */
 QWidget *ICore::currentContextWidget()
 {
@@ -2300,7 +2300,7 @@ QList<IContext *> ICore::contextObjects(QWidget *widget)
 
     \sa removeContextObject()
     \sa updateAdditionalContexts()
-    \sa currentContextObject()
+    \sa currentContextObjects()
     \sa {The Action Manager and Commands}
 */
 
@@ -2319,7 +2319,7 @@ void ICore::addContextObject(IContext *context)
 
     \sa addContextObject()
     \sa updateAdditionalContexts()
-    \sa currentContextObject()
+    \sa currentContextObjects()
 */
 
 void ICore::removeContextObject(IContext *context)