This restores the ability to leave out the initial context parameter
when defining functions with reflection. This is important because some
projects are porting from a different library to wazero, and all the
alternatives are not contextualized.
For example, this project is porting envoy host functions, and the
original definitions (in mosn) don't have a context parameter. By being
lenient, they can migrate easier.
See 6b813482b6/pkg/proxywasm/wazero/imports_v1.go
Signed-off-by: Adrian Cole <adrian@tetrate.io>