Remove some custom error types in Wasmtime (#5347)

* Remove some custom error types in Wasmtime

These types are mostly cumbersome to work with nowadays that `anyhow` is
used everywhere else. This commit removes `InstantiationError` and
`SetupError` in favor of using `anyhow::Error` throughout. This can
eventually culminate in creation of specific errors for embedders to
downcast to but for now this should be general enough.

* Fix Windows build

tests/all/pooling_allocator.rs

@@ -428,7 +428,7 @@ fn instantiation_limit() -> Result<()> {
             Err(e) => assert_eq!(
                 e.to_string(),
                 format!(
-                    "Limit of {} concurrent instances has been reached",
+                    "maximum concurrent instance limit of {} reached",
                     INSTANCE_LIMIT
                 )
             ),