Reduce IL size in `generator` output

[jonathanpeppers]

Introduced in:

• [generator] Eliminate usage of JNINativeWrapper.CreateDelegate in bindings. #1275

This caused IL size to grow by about 200k for Mono.Android.dll, such as:

> (ls "C:\Users\jopepper\Desktop\android\net10-linked-no-mm\Mono.Android.dll").Length
1780224
> (ls "C:\Users\jopepper\Desktop\android\net10-linked\Mono.Android.dll").Length
1798656
> (ls "C:\Users\jopepper\Desktop\android\net9-linked\Mono.Android.dll").Length
1590272

We think this could be improved by making a couple helper methods to reduce the IL emitted.

@simonrozsival had an idea for an implementation here.