Update markdown generator for world inputs (#393)

This commit migrates the markdown generator from the `Generator` trait
of old to the new `WorldGenerator` trait which operates on a
`ComponentInterfaces` and takes a "world" as first-class input.

Author: alexcrichton

Cargo.lock

@@ -12,3 +12,4 @@ heck = { workspace = true }
 pulldown-cmark = { workspace = true }
 clap = { workspace = true, optional = true }
 wit-bindgen-core = { workspace = true }
+wit-component = { workspace = true }