fix: formula cannot contain matched curly braces in strings

Describe the bug

When a string in the expression of a formula field contains matched curly braces, i.e. { ... }, with arbitrary contents between the braces, an invalid column or funciton name error is reported.

To Reproduce

1. Open the field setting panel of an existing formula field.
2. Modify its expression to '{ }'.
3. An invalid column or function name error is reported.

Expected behavior

No error is reported for expressions like '{ }'.

Screenshots