CMake: Make use of CMake-provided .qch files

* Have UI to select a .qch file location in CMake Tool setup
* Auto-detect CMake's .qch file in its default location (relative
  to the cmake executable)
* Register the .qch files with the HelpManager

Task-number: QTCREATORBUG-21338
Change-Id: I4057eec42c39535012d9f0daf788fc62ef20d544
Reviewed-by: hjk <hjk@qt.io>

src/plugins/cmakeprojectmanager/cmaketoolmanager.cpp

@@ -27,6 +27,7 @@
 
 #include "cmaketoolsettingsaccessor.h"
 
+#include <coreplugin/helpmanager.h>
 #include <coreplugin/icore.h>
 
 #include <utils/pointeralgorithm.h>
@@ -105,6 +106,8 @@ bool CMakeToolManager::registerCMakeTool(std::unique_ptr<CMakeTool> &&tool)
 
     ensureDefaultCMakeToolIsValid();
 
+    updateDocumentation();
+
     return true;
 }
 
@@ -112,9 +115,10 @@ void CMakeToolManager::deregisterCMakeTool(const Id &id)
 {
     auto toRemove = Utils::take(d->m_cmakeTools, Utils::equal(&CMakeTool::id, id));
     if (toRemove.has_value()) {
-
         ensureDefaultCMakeToolIsValid();
 
+        updateDocumentation();
+
         emit m_instance->cmakeRemoved(id);
     }
 }
@@ -152,9 +156,22 @@ void CMakeToolManager::restoreCMakeTools()
     d->m_cmakeTools = std::move(tools.cmakeTools);
     setDefaultCMakeTool(tools.defaultToolId);
 
+    updateDocumentation();
+
     emit m_instance->cmakeToolsLoaded();
 }
 
+void CMakeToolManager::updateDocumentation()
+{
+    const QList<CMakeTool *> tools = cmakeTools();
+    QStringList docs;
+    for (const auto tool : tools) {
+        if (!tool->qchFilePath().isEmpty())
+            docs.append(tool->qchFilePath().toString());
+    }
+    Core::HelpManager::registerDocumentation(docs);
+}
+
 void CMakeToolManager::notifyAboutUpdate(CMakeTool *tool)
 {
     if (!tool || !Utils::contains(d->m_cmakeTools, tool))