Fix lexical scoping between scripts (#3558)

This change fixes the handling of lexical blocks when executing multiple
scripts, and also fixes a few issues with module environments.

After this change, all script files will run in the same context and
will have access to lexically scoped global variables of previous
scripts, and module environments will no longer have a bound global
'this' value.

The REPL implementation in main-unix is also fixed to correctly handle
lexically scoped variables.

Fixes #3561.

JerryScript-DCO-1.0-Signed-off-by: Dániel Bátyai dbatyai@inf.u-szeged.hu

jerry-core/vm/vm.h

@@ -229,6 +229,8 @@ typedef enum
   VM_OC_LINE,                    /**< line number of the next statement */
 #endif /* ENABLED (JERRY_LINE_INFO) */
 #if ENABLED (JERRY_ES2015)
+  VM_OC_CHECK_VAR,               /**< check redeclared vars in the global scope */
+  VM_OC_CHECK_LET,               /**< check redeclared lets in the global scope */
   VM_OC_ASSIGN_LET_CONST,        /**< assign values to let/const declarations */
   VM_OC_COPY_TO_GLOBAL,          /**< copy value to global lex env */
   VM_OC_CLONE_CONTEXT,           /**< clone lexical environment with let/const declarations */
@@ -286,6 +288,8 @@ typedef enum
   VM_OC_LINE = VM_OC_NONE,                    /**< line number of the next statement is unused */
 #endif /* !ENABLED (JERRY_LINE_INFO) */
 #if !ENABLED (JERRY_ES2015)
+  VM_OC_CHECK_VAR = VM_OC_NONE,               /**< check redeclared vars in the global scope */
+  VM_OC_CHECK_LET = VM_OC_NONE,               /**< check redeclared lets in the global scope */
   VM_OC_ASSIGN_LET_CONST = VM_OC_NONE,        /**< assign values to let/const declarations */
   VM_OC_COPY_TO_GLOBAL = VM_OC_NONE,          /**< copy value to global lex env */
   VM_OC_CLONE_CONTEXT = VM_OC_NONE,           /**< clone lexical environment with let/const declarations */