Updated Blazor macOS Catalina/iOS 13 workaround (#14576)

* MacOSX Catalina Beta wasm workaround for booting mono wasm from Blazor.

* Address review comments

* Address review comments

* Make it clear why global scope is used.

* Stylistic tweaks for Catalina workaround

* Further streamlining

* Update js binaries

Author: SteveSandersonMS