Fix: make jerryx_module_resolve resolvers argument const (#1942)

The resolvers argument that is passed to jerryx_module_resolve() is
not mutated by the function. Therefore the argument should be const.
In the docs, a static const array is passed, but this currently does not
work w/o a cast. This patch fixes this.

JerryScript-DCO-1.0-Signed-off-by: Martijn The martijn.the@intel.com

tests/unit-ext/module/jerry-module-test.c

@@ -91,7 +91,7 @@ cache_check (const jerry_char_t *name,
   return false;
 } /* cache_check */
 
-static jerryx_module_resolver_t resolvers[3] =
+static const jerryx_module_resolver_t resolvers[3] =
 {
   jerryx_module_native_resolver,
   resolve_differently_handled_module,