Doc: Add textual descriptions for QtBluetooth documentation images

Added textual descriptions to images in the QtBluetooth documentation
to ensure QDoc generates alt text.

Fixes: QTBUG-136156
Change-Id: I94ffbb6cb713ac3141f229c9c18e9bc2bd94185c
Reviewed-by: Axel Spoerl <axel.spoerl@qt.io>
(cherry picked from commit f63823f4de)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
(cherry picked from commit 4a9d2068ed)

examples/bluetooth/btchat/doc/src/btchat.qdoc

@@ -10,7 +10,7 @@
     The Bluetooth Chat example shows how to use the \l{Qt Bluetooth} API to communicate
     with another application on a remote device using Bluetooth RFCOMM protocol.
 
-    \image btchat-example.png
+    \image {btchat-example.png} {Qt Bluetooth chat UI}
 
     The Bluetooth Chat example implements a simple chat program between multiple parties. The
     application always acts as both a server and a client eliminating the need to determine who

examples/bluetooth/heartrate-game/doc/src/heartrate-game.qdoc

@@ -15,7 +15,7 @@
     characteristics and descriptors, and receiving updates from the device once the heart rate
     has changed.
 
-    \image heartgame-start.webp
+    \image {heartgame-start.webp} {Start screen of Qt Heart Game}
 
     The example introduces the following Qt classes:
 
@@ -61,17 +61,17 @@
     presented in a list. Note that all found Bluetooth Low Energy devices are listed even
     if they do not offer a Heart Rate service.
 
-    \image heartgame-search.webp
+    \image {heartgame-search.webp} {Qt Heart Game scanning for Bluetooth devices}
 
     After the user has selected a target device, the example connects to its Heart Rate service
     if one is available. It automatically enables notification updates for the Heart Rate value
     and presents the current value on the screen.
 
-    \image heartgame-running.webp
+    \image {heartgame-running.webp} {Gameplay screen of the Qt Heart Game}
 
     Once the monitoring process is finished, a small summary of the received
     values is presented.
 
-    \image heartgame-result.webp
+    \image {heartgame-result.webp} {Qt Heart Game result screen}
 
 */

examples/bluetooth/lowenergyscanner/doc/src/lowenergyscanner.qdoc

@@ -16,7 +16,7 @@
     scanning for Low Energy devices, scanning their services and reading
     the service characteristics and descriptors.
 
-    \image lowenergyscanner-services.png
+    \image {lowenergyscanner-services.png} {GATT services found using Qt BLE scanner}
 
     The example introduces the following Qt classes:
 
@@ -74,7 +74,7 @@
     The list of devices may look like in the image below. \note It is a prerequisite
     that the remote devices actively advertise their presence.
 
-    \image lowenergyscanner-devices.png
+    \image {lowenergyscanner-devices.png} {Nearby devices listed in Qt BLE scanner}
 
     \section1 Connecting to Services
 
@@ -96,7 +96,7 @@
     device is selected. The view lists the names of the services, whether they are
     primary or secondary services and the UUID which determines the service type.
 
-    \image lowenergyscanner-services.png
+    \image {lowenergyscanner-services.png} {GATT services found using Qt BLE scanner}
 
     As soon as the service is chosen the related \l QLowEnergyService instance is created to
     permit interaction with it:
@@ -119,7 +119,7 @@
     Upon selection of a service the service details are shown. Each characteristic
     is listed together with its name, UUID, value, handle and properties.
 
-    \image lowenergyscanner-chars.png
+    \image {lowenergyscanner-chars.png} {GATT characteristics listed in Qt BLE Scanner}
 
     It is possible to retrieve the service's characteristics via
     \l QLowEnergyService::characteristics() and in turn, each descriptor can be obtained

src/bluetooth/doc/src/bluetooth-le-overview.qdoc

@@ -128,7 +128,7 @@ Low Energy devices.
     descriptors are recognized by their 128-bit UUID. Finally, it is possible to include
     services inside of services (see picture below).
 
-    \image peripheral-structure.png
+    \image {peripheral-structure.png} {Structure of a BLE peripheral in Qt}
 
     \section1 Using Qt Bluetooth Low Energy API