support enums with more than 256 variants in derive macro (#4370)

* support enums with more than 256 variants in derive macro

This addresses #4361.  Technically, we now support up to 2^32 variants, which is
the maximum for the canonical ABI.  In practice, though, the derived code for
enums with even just 2^16 variants takes a prohibitively long time to compile.

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

* simplify `LowerExpander::expand_variant` code

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

Cargo.toml

@@ -60,6 +60,7 @@ async-trait = "0.1"
 wat = "1.0.43"
 once_cell = "1.9.0"
 rayon = "1.5.0"
+component-macro-test = { path = "crates/misc/component-macro-test" }
 
 [target.'cfg(windows)'.dev-dependencies]
 windows-sys = { version = "0.36.0", features = ["Win32_System_Memory"] }