do not clear Task definition or scope unless execution changes

- in the current Task class of the plugin-ext package, the "definition" and "scope" property are reset if any Task property gets updated. Since the "task definition" is only dependent on "task execution", this change updates the value of "task definition" if and only if "task execution" is changed.

Signed-off-by: elaihau <liang.huang@ericsson.com>

packages/plugin-ext/src/plugin/types-impl.ts

@@ -1536,7 +1536,6 @@ export class Task {
         if (value === undefined || value === null) {
             throw illegalArgument('Kind can\'t be undefined or null');
         }
-        this.clear();
         this.taskDefinition = value;
     }
 
@@ -1545,7 +1544,6 @@ export class Task {
     }
 
     set scope(value: theia.TaskScope.Global | theia.TaskScope.Workspace | theia.WorkspaceFolder | undefined) {
-        this.clear();
         this.taskScope = value;
     }
 
@@ -1557,7 +1555,6 @@ export class Task {
         if (typeof value !== 'string') {
             throw illegalArgument('name');
         }
-        this.clear();
         this.taskName = value;
     }
 
@@ -1569,7 +1566,7 @@ export class Task {
         if (value === null) {
             value = undefined;
         }
-        this.clear();
+        this.updateDefinitionBasedOnExecution();
         this.taskExecution = value;
     }
 
@@ -1583,7 +1580,6 @@ export class Task {
             this.hasTaskProblemMatchers = false;
             return;
         }
-        this.clear();
         this.taskProblemMatchers = value;
         this.hasTaskProblemMatchers = true;
     }
@@ -1600,7 +1596,6 @@ export class Task {
         if (value !== true && value !== false) {
             value = false;
         }
-        this.clear();
         this.isTaskBackground = value;
     }
 
@@ -1612,7 +1607,6 @@ export class Task {
         if (typeof value !== 'string' || value.length === 0) {
             throw illegalArgument('source must be a string of length > 0');
         }
-        this.clear();
         this.taskSource = value;
     }
 
@@ -1625,7 +1619,6 @@ export class Task {
             this.taskGroup = undefined;
             return;
         }
-        this.clear();
         this.taskGroup = value;
     }
 
@@ -1637,12 +1630,10 @@ export class Task {
         if (value === null) {
             value = undefined;
         }
-        this.clear();
         this.taskPresentationOptions = value;
     }
 
-    private clear(): void {
-        this.taskScope = undefined;
+    private updateDefinitionBasedOnExecution(): void {
         this.taskDefinition = undefined;
         if (this.taskExecution instanceof ProcessExecution) {
             this.taskDefinition = {