[mono][wasm] MacOSX Catalina Beta wasm workaround for booting mono wasm from Blazor.

[kjpou1]

Summary of the changes (Less than 80 chars)

• MacOSX Catalina initializes WebAssembly Module differently and needs to be initialized before loading mono.js.

Modifications:

• Add new method to MonoPlatform.ts addGlobalModuleScriptTagsToDocument
  • Make sure we have the Module defined from the page as a <script></script> tag
  • When the Module is defined the regular Blazor mono webassembly setup is followed.
• Boot start modified to call the new method addGlobalModuleScriptTagsToDocument.

After modification:

• New <script></script> is added to the page that defines the WebAssembly Module before the addition of the <script></script> tag to load mono.js.

[SteveSandersonMS]

Thanks very much for this, @kjpou1!

Before I proceed with merging this, could you please comment about this comment:

// Make sure we have the Module setup from the page due to a difference in MacOSX Catalina Beta.
// This may not be necassary in the Catalina release.

Now that iOS 13 (and even 13.1) have shipped, could you confirm whether or not this workaround is still needed? If it is then presumably we can update this comment not to say "may not be necessary".

[kg]

Following the current tutorial steps on the Blazor website on Catalina + Safari 13, nothing works so I suspect these changes are still necessary.

I'll be doing some more troubleshooting to confirm.

[SteveSandersonMS]

Thanks again for this. We're about to merge it, so I needed to make a couple of further tweaks. So, closing this in favour of #14576 which adds those tweaks.