createDescriptorChangeString(mPropertyBag) {
			return this.createDescriptorInlineChanges(mPropertyBag)
			.then(function(oChange) {
				var oSimpleChange = _pick(oChange.getJson(), ["changeType", "content", "texts"]);
				return Promise.resolve(JSON.stringify(oSimpleChange));
			});
		}
Creates a descriptor inline change as string.
This string can be collected and later passed to the ABAP API /ui5/cl_app_variant_api

@param {object} mPropertyBag - Object with parameters as properties
@param {string} mPropertyBag.appId - Reference app ID or an app variant ID
@param {object} mPropertyBag.changeSpecificData - Property bag holding the change information
The property <code>mPropertyBag.changeSpecificData.packageName</code> is set to <code>$TMP</code>
and internally since flex changes are always local when they are created.

@returns {Promise<string>} Promise resolves with a string of simplified DescriptorInlineChange
@private
@ui5-restricted