wasmtime: Extract cranelift/lightbeam compilers to separate crates (#2117)

This commit extracts the two implementations of `Compiler` into two
separate crates, `wasmtime-cranelfit` and `wasmtime-lightbeam`. The
`wasmtime-jit` crate then depends on these two and instantiates them
appropriately. The goal here is to start reducing the weight of the
`wasmtime-environ` crate, which currently serves as a common set of
types between all `wasmtime-*` crates. Long-term I'd like to remove the
dependency on Cranelift from `wasmtime-environ`, but that's going to
take a lot more work.

In the meantime I figure it's a good way to get started by separating
out the lightbeam/cranelift function compilers from the
`wasmtime-environ` crate. We can continue to iterate on moving things
out in the future, too.

Cargo.lock

@@ -2414,6 +2414,17 @@ dependencies = [
  "wat",
 ]
 
+[[package]]
+name = "wasmtime-cranelift"
+version = "0.19.0"
+dependencies = [
+ "cranelift-codegen",
+ "cranelift-entity",
+ "cranelift-frontend",
+ "cranelift-wasm",
+ "wasmtime-environ",
+]
+
 [[package]]
 name = "wasmtime-debug"
 version = "0.19.0"
@@ -2436,11 +2447,9 @@ dependencies = [
  "cfg-if",
  "cranelift-codegen",
  "cranelift-entity",
- "cranelift-frontend",
  "cranelift-wasm",
  "gimli 0.21.0",
  "indexmap",
- "lightbeam",
  "log",
  "more-asserts",
  "serde",
@@ -2500,14 +2509,26 @@ dependencies = [
  "target-lexicon",
  "thiserror",
  "wasmparser 0.59.0",
+ "wasmtime-cranelift",
  "wasmtime-debug",
  "wasmtime-environ",
+ "wasmtime-lightbeam",
  "wasmtime-obj",
  "wasmtime-profiling",
  "wasmtime-runtime",
  "winapi",
 ]
 
+[[package]]
+name = "wasmtime-lightbeam"
+version = "0.19.0"
+dependencies = [
+ "cranelift-codegen",
+ "lightbeam",
+ "wasmparser 0.59.0",
+ "wasmtime-environ",
+]
+
 [[package]]
 name = "wasmtime-obj"
 version = "0.19.0"