implement fuzzing for component types (#4537)

This addresses #4307.

For the static API we generate 100 arbitrary test cases at build time, each of
which includes 0-5 parameter types, a result type, and a WAT fragment containing
an imported function and an exported function.  The exported function calls the
imported function, which is implemented by the host.  At runtime, the fuzz test
selects a test case at random and feeds it zero or more sets of arbitrary
parameters and results, checking that values which flow host-to-guest and
guest-to-host make the transition unchanged.

The fuzz test for the dynamic API follows a similar pattern, the only difference
being that test cases are generated at runtime.

Signed-off-by: Joel Dice <joel.dice@fermyon.com>

build.rs

@@ -41,7 +41,7 @@ fn main() -> anyhow::Result<()> {
             } else {
                 println!(
                     "cargo:warning=The spec testsuite is disabled. To enable, run `git submodule \
-                 update --remote`."
+                     update --remote`."
                 );
             }
             Ok(())