Upcast and downcast are switched

[danaugrs]

Hi! Thanks for building AssemblyScript! I noticed that "upcast" and "downcast" are switched:

https://github.com/AssemblyScript/assemblyscript/blob/53af0e02113f0c4cd84947465a8c5064d3a82786/src/compiler.ts#L3472-L3501

"Upcast" should be the straightforward, static case whereas "downcast" should be dynamic and more complex. No logic changes are needed, just the words need to be switched, especially in the error message below:

https://github.com/AssemblyScript/assemblyscript/blob/53af0e02113f0c4cd84947465a8c5064d3a82786/src/compiler.ts#L10564

For context, that error message was pointed out to be wrong in https://github.com/LimeChain/demo-subgraph/pull/39.

I created a PR to fix this issue: https://github.com/AssemblyScript/assemblyscript/pull/2423.

[MaxGraey]

Looks like managed-cast test still fail