Allow new lines to be entered when editing textareas (#633)

Previously, new lines could not be entered when using textareas for the
textfield component (i.e setting multiline: true on
the muiEditTextFieldProps prop). This change allows the user to enter
new lines when using textareas.

packages/material-react-table/src/inputs/MRT_EditCellTextField.tsx

@@ -82,7 +82,7 @@ export const MRT_EditCellTextField = <TData extends Record<string, any>>({
 
   const handleEnterKeyDown = (event: KeyboardEvent<HTMLInputElement>) => {
     textFieldProps.onKeyDown?.(event);
-    if (event.key === 'Enter') {
+    if (event.key === 'Enter' && !event.shiftKey) {
       editInputRefs.current[column.id]?.blur();
     }
   };