Python: Avoid polluting global or virtual environments with pylsp

Install the language server into the Qt Creator resource directory
instead. Reuse the server for all interpreters with the same
version. This also reduces the amount of editor toolbars asking the user
to install a language server for a specific interpreter.

Change-Id: I48ef4ad30fe0097ee8d2b855b0f278e98be5ce57
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/python/pipsupport.h

@@ -67,6 +67,7 @@ public:
     void setWorkingDirectory(const Utils::FilePath &workingDirectory);
     void addPackage(const PipPackage &package);
     void setPackages(const QList<PipPackage> &packages);
+    void setTargetPath(const Utils::FilePath &targetPath);
     void run();
 
 signals:
@@ -83,6 +84,7 @@ private:
     const Utils::FilePath m_python;
     QList<PipPackage> m_packages;
     Utils::FilePath m_requirementsFile;
+    Utils::FilePath m_targetPath;
     Utils::Process m_process;
     QFutureInterface<void> m_future;
     QFutureWatcher<void> m_watcher;