runtime + codegen-js: Promise helpers and object/array utilities

Add to el_runtime.js:
  promise_then(p, cb)    -- p.then(cb), works with any Promise-returning API
  promise_catch(p, cb)   -- p.catch(cb)
  promise_resolve(val)   -- Promise.resolve(val)
  promise_reject(msg)    -- Promise.reject(new Error(msg))
  object_assign(t, s)    -- Object.assign({}, t, s) (non-mutating)
  object_keys(obj)       -- Object.keys(obj)
  object_values(obj)     -- Object.values(obj)
  json_deep_clone(obj)   -- JSON.parse(JSON.stringify(obj))
  array_from(iterable)   -- Array.from(iterable)
  type_of(val)           -- typeof val
  instanceof_check(v, n) -- val instanceof globalThis[name]

All new functions added to __el export object and ES named exports.
codegen-js preamble destructure updated to include all new names.

el-compiler/src/codegen-js.el

@@ -1105,6 +1105,9 @@ fn codegen_js_inner(stmts: [Map<String, Any>], source: String, bundle_mode: Bool
         js_emit_line("  window_location, window_redirect, window_on_load,")
         js_emit_line("  console_log,")
         js_emit_line("  window_set, window_get, native_js, native_js_call,")
+        js_emit_line("  promise_then, promise_catch, promise_resolve, promise_reject,")
+        js_emit_line("  object_assign, object_keys, object_values, json_deep_clone,")
+        js_emit_line("  array_from, type_of, instanceof_check,")
         js_emit_line("} = globalThis.__el;")
         js_emit_blank()
     }