fix: Fix temp. local confusion in indexed assignment compilation (#1703)

Author: petersalomonsen

NOTICE

@@ -33,6 +33,7 @@ under the licensing terms detailed in LICENSE:
 * Piotr Oleś <piotrek.oles@gmail.com>
 * Saúl Cabrera <saulecabrera@gmail.com>
 * Chance Snow <git@chancesnow.me>
+* Peter Salomonsen <petersalomonsen@runbox.com>
 
 Portions of this software are derived from third-party works licensed under
 the following terms:

src/compiler.ts

@@ -5988,7 +5988,6 @@ export class Compiler extends DiagnosticEmitter {
           let tempTarget = flow.getTempLocal(thisType);
           let tempElement = flow.getTempLocal(elementType);
           let returnType = getterInstance.signature.returnType;
-          flow.freeTempLocal(tempTarget);
           let ret = module.block(null, [
             this.makeCallDirect(setterInstance, [
               module.local_tee(tempTarget.index, thisExpr, thisType.isManaged),

tests/compiler/issues/1699.optimized.wat

@@ -0,0 +1,19 @@
+class MultiAssignmentTest {
+    test: i32 = 2;
+}
+
+function test(): void {
+  const testinstances = new Array<MultiAssignmentTest>(3);
+  testinstances[0] = testinstances[1] = new MultiAssignmentTest();
+
+  for (let n = 0; n < testinstances.length; n++) {
+    const testinstance = new MultiAssignmentTest();
+    if (n > 1) {
+      testinstances[n] = testinstance;
+    }
+  }
+  assert(testinstances[0] === testinstances[1]);
+  assert(testinstances[2] !== testinstances[1]);
+}
+
+test();