Correctly handle ^1 in expressions.js

Test plan:
Verify question is displayed correctly in http://localhost:8000/exercises/simplifying_expressions_with_exponents.html?seed=6&problem=simplify-exponential-form-mini&debug

fix #42543; fix #42484; fix #42482; fix #42455; fix #42391; fix #42365;
fix #42361; fix #42326; fix #42316; fix #42312; fix #42276; fix #42257;
fix #42241

Auditors: alpert