[INTERNAL] Rename environment variable to UI5_LOG_TASK_PERF for activating perfomance measurement (#748)

By using the environment variable UI5_LOG_TASK_PERF=true the processing time of a task is calculated and written to the log.
Rename the variable from UI5_PERF_TASK to UI5_LOG_TASK_PERF.
BLI: CPOUI5FOUNDATION-497

Author: flovogt

lib/types/AbstractBuilder.js

@@ -238,7 +238,7 @@ class AbstractBuilder {
 		this._taskStart = performance.now();
 		await taskFunction();
 		this.taskLog.completeWork(1);
-		if (process.env.UI5_PERF_TASK) {
+		if (process.env.UI5_LOG_TASK_PERF) {
 			this.taskLog.info(`Task succeeded in ${Math.round((performance.now() - this._taskStart))} ms`);
 		}
 	}