wasi-common: switch all logs from log to tracing

tracing is already the dep that wiggle uses.

I used tracing structured arguments wherever I could, but I skipped over
it in all of the snapshot_0 code, because I'm going to delete that code
and replace it with wiggle-based stuff real soon.

Cargo.lock

@@ -2324,8 +2324,8 @@ dependencies = [
  "getrandom",
  "lazy_static",
  "libc",
- "log",
  "thiserror",
+ "tracing",
  "wig",
  "wiggle",
  "winapi",
@@ -2629,7 +2629,7 @@ name = "wasmtime-wasi"
 version = "0.19.1"
 dependencies = [
  "anyhow",
- "log",
+ "tracing",
  "wasi-common",
  "wasmtime",
  "wasmtime-runtime",