Optional computed member expressions are not supported (add validation)

We don't propagate the `optional` flag through to codegen, so let's error on 
this for now

compiler/forget/src/HIR/BuildHIR.ts

@@ -1744,6 +1744,13 @@ function lowerMemberExpression(
         },
       };
     }
+    if (t.isOptionalMemberExpression(expr)) {
+      builder.errors.push({
+        reason: `(BuildHIR::lowerMemberExpression) Handle computed OptionalMemberExpression`,
+        severity: ErrorSeverity.Todo,
+        nodePath: expr,
+      });
+    }
     const propertyPlace = lowerExpressionToTemporary(builder, property);
     const value: InstructionValue = {
       kind: "ComputedLoad",

compiler/forget/src/__tests__/fixtures/compiler/error.optional-computed-member-expression.expect.md

@@ -0,0 +1,25 @@
+
+## Input
+
+```javascript
+function Component(props) {
+  const object = makeObject(props);
+  return object?.[props.key];
+}
+
+```
+
+
+## Error
+
+```
+[ReactForget] TodoError: (BuildHIR::lowerMemberExpression) Handle computed OptionalMemberExpression
+  1 | function Component(props) {
+  2 |   const object = makeObject(props);
+> 3 |   return object?.[props.key];
+    |          ^^^^^^^^^^^^^^^^^^^
+  4 | }
+  5 |
+```
+          
+      

compiler/forget/src/__tests__/fixtures/compiler/error.optional-computed-member-expression.js

@@ -0,0 +1,4 @@
+function Component(props) {
+  const object = makeObject(props);
+  return object?.[props.key];
+}