[js_interop, dart2js] Ensure static js_interop is efficient with dart2js

[rakudrama]

This is a tracking issue to label changes made to ensure static js_interop is efficient for dart2js.

Progress before this issue was created:

ed54a42 - add a benchmark for some operations
3bedcdf - using synthesized static getters rather than lowering the call so that the getter can retain annotations.
20e8977 - makes as JSObject faster (mainly helps -O2 rather than production, also helps DDC)