Add root project folder to each key in projectTreeItemMap

In microsoft#1612, the keys of this map were changed to the Gradle project path.
This path is unique for each project within one Gradle build, but not
if there are multiple Gradle builds loaded in one workspace by using:
'gradle.nestedProjects': true

This change combined the old and new behavior by creating the Map key
from two parts:
(1) The root project folder which uniquely identifies the build
    (accessible via definition.projectFolder)
(2) The Gradle project path that uniquely identifies a project inside
    the build

Author: jjohannes

extension/src/views/gradleTasks/GradleTasksTreeDataProvider.ts

@@ -254,13 +254,14 @@ export class GradleTasksTreeDataProvider implements vscode.TreeDataProvider<vsco
                 }
 
                 const projectPath = definition.script.split(":").slice(0, -1);
-                let projectTreeItem = projectTreeItemMap.get(projectPath.join(":"));
+                const projectMapKey = definition.projectFolder + "_" + projectPath.join(":");
+                let projectTreeItem = projectTreeItemMap.get(projectMapKey);
                 if (!projectTreeItem) {
                     const parentProjectPath = projectPath.length == 0 ? null : projectPath.slice(0, -1);
                     const parentProject =
                         parentProjectPath === null
                             ? gradleProjectTreeItem
-                            : projectTreeItemMap.get(parentProjectPath.join(":"));
+                            : projectTreeItemMap.get(definition.projectFolder + "_" + parentProjectPath.join(":"));
                     projectTreeItem = new ProjectTreeItem(
                         definition.project,
                         parentProject,
@@ -271,7 +272,7 @@ export class GradleTasksTreeDataProvider implements vscode.TreeDataProvider<vsco
                     } else {
                         gradleProjectTreeItem.addProject(projectTreeItem);
                     }
-                    projectTreeItemMap.set(projectPath.join(":"), projectTreeItem);
+                    projectTreeItemMap.set(projectMapKey, projectTreeItem);
                 }
 
                 const taskName = definition.script.slice(definition.script.lastIndexOf(":") + 1);
@@ -309,4 +310,8 @@ export class GradleTasksTreeDataProvider implements vscode.TreeDataProvider<vsco
         }
         return [...gradleProjectTreeItemMap.values()];
     }
+
+    private projectTreeItemMapKey(rootProjectFolder: string, gradleProjectPath: string) {
+        return rootProjectFolder + "_" + gradleProjectPath;
+    }
 }