wit/bindgen: improve WIT world matching, warn if ambiguous

[ydnar]

Sort WIT packages topologically by dependency before matching WIT world when generating Go bindings. Warn if there is an ambiguous match.

Fixes #356.

$ go tool go.bytecodealliance.org/cmd/wit-bindgen-go generate -v -w imports -o bindings wit
Output dir: bindings
Package root: github.com/rvolosatovs/go-bindgen-repro/bindings
WIT world: repro:repro/imports@0.1.0
Warning: ambiguous WIT world: wasi:http/imports@0.2.1
Warning: ambiguous WIT world: wasi:cli/imports@0.2.1
Warning: ambiguous WIT world: wasi:filesystem/imports@0.2.1
Warning: ambiguous WIT world: wasi:random/imports@0.2.1
Warning: ambiguous WIT world: wasi:sockets/imports@0.2.1
Warning: ambiguous WIT world: wasi:clocks/imports@0.2.1
Warning: ambiguous WIT world: wasi:io/imports@0.2.1