optimize fillStyle to be 10% faster

this is possibly a hot path, and avoiding the C++ string helps a
little bit

CHANGELOG.md

@@ -13,6 +13,7 @@ project adheres to [Semantic Versioning](http://semver.org/).
 * Migrate from librsvg's deprecated `rsvg_handle_get_dimensions()` and `rsvg_handle_render_cairo()` functions to the new `rsvg_handle_get_intrinsic_size_in_pixels()` and `rsvg_handle_render_document()` respectively. (#2229)
 * Avoid calling virtual methods in constructors/destructors to avoid bypassing virtual dispatch. (#2229)
 * Remove unused private field `backend` in the `Backend` class. (#2229)
+* Migrated to N-API (by way of node-addon-api) and removed libuv and v8 dependencies
 ### Added
 * Added string tags to support class detection
 ### Fixed

src/CanvasRenderingContext2d.cc

@@ -2138,8 +2138,11 @@ Context2d::_setFillColor(Napi::Value arg) {
   short ok;
 
   if (stringValue.IsJust()) {
-    std::string str = stringValue.Unwrap().Utf8Value();
-    uint32_t rgba = rgba_from_string(str.c_str(), &ok);
+    Napi::String str = stringValue.Unwrap();
+    char buf[128] = {0};
+    napi_status status = napi_get_value_string_utf8(env, str, buf, sizeof(buf) - 1, nullptr);
+    if (status != napi_ok) return;
+    uint32_t rgba = rgba_from_string(buf, &ok);
     if (!ok) return;
     state->fillPattern = state->fillGradient = NULL;
     state->fill = rgba_create(rgba);