Extract jit_int.rs and most of jitdump_linux.rs for use outside of wasmtime (#2744)

* Extract gdb jit_int into wasmtime-jit-debug

* Move a big chunk of the jitdump code to wasmtime-jit-debug

* Fix doc markdown in perf_jitdump.rs

crates/jit-debug/src/lib.rs

@@ -0,0 +1,5 @@
+#[cfg(feature = "gdb_jit_int")]
+pub mod gdb_jit_int;
+
+#[cfg(all(feature = "perf_jitdump", target_os = "linux"))]
+pub mod perf_jitdump;