Optimize lexenv binding creation (#4502)

- Declarative environment no longer need to lookup the created binding for setting it's value
- Unfold vm_decl_var and vm_set_var into vm_loop to reduce error checks
- Reduce code duplication in ecma_module_connect_imports
- Fix deleted binding setting in `ecma_op_set_mutable_binding` (fixes #4468)

JerryScript-DCO-1.0-Signed-off-by: Robert Fancsik frobert@inf.u-szeged.hu

tests/jerry/es.next/regression-test-issue-4468.js

@@ -0,0 +1,17 @@
+// Copyright JS Foundation and other contributors, http://js.foundation
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+var str = 'for (let i=0; i<(eval("1; function x() { }; 2;")); x - i++) { x += delete x;}'
+
+assert(eval(str) === 'function(){/* ecmascript */}true');