isDynamicName skips parentheses for element access

Neither `x[0]` nor `x[(0)]` should be dynamic names. Previously, the
latter was because `isDynamicName` didn't skip parentheses.

Since the binder treats dynamic names in property assignments as
assignment declarations, this incorrectly tried to create a binding for
expressions like `x[(0)] = 1`.

This caused an assert because `x[(0)]` would not take the dynamic name
code path during binding (`hasDynamicName` returned false), but the
normal code path for static names.

tests/cases/conformance/salsa/propertyAssignmentOnParenthesizedNumber.ts

@@ -0,0 +1,8 @@
+// @allowJs: true
+// @checkJs: true
+// @noEmit: true
+// @Filename: bug38934.js
+
+var x = {};
+// should not crash and also should not result in a property '0' on x.
+x[(0)] = 1;