Factors trigger

[lann]

This turned into a bit of a mega-PR, but I have split out some smaller commits, including:

• Add SpinFilesMounter
• Add intermediate FactorsExecutorApp type

Note that while this mostly a straight port, I have also implemented 2 breaking changes for Spin 3.0:

• Drop support for executing WAGI modules
  • still need to fix up detection and errors for uncomponentizable modules
• Drop the HTTP trigger base field
  • the default value of / is still permitted with a warning

I've left the existing spin-trigger and spin-trigger-http crates for now as there is still some functionality that needs to be ported to factors:

• Outbound HTTP features that were implemented in spin-trigger-http: client TLS, self and service chained requests
• spin-trigger-http benchmarks

[rylev]

👀

[rylev]

This is when things start to get a bit scary - the trigger2 crate has a lot of overlap with the existing trigger crate, and it's hard to see where things differ. I think we're at the point that I'd like to see integration of factors happened as quickly as possible so we stop living in a world where things can easily diverge.

[rylev]

It'd be good to document what this is - an HttpExector that can execute wasi and spin http incoming requests.

[lann]

This is when things start to get a bit scary - the trigger2 crate has a lot of overlap with the existing trigger crate, and it's hard to see where things differ. I think we're at the point that I'd like to see integration of factors happened as quickly as possible so we stop living in a world where things can easily diverge.

Agreed. I've been struggling with a more principled refactor here and at this point I just want to get something merged to build on.