Move trap information to a section of the compiled image (#3241)

This commit moves the `traps` field of `FunctionInfo` into a section of
the compiled artifact produced by Cranelift. This section is quite large
and when previously encoded/decoded with `bincode` this can take quite
some time to process. Traps are expected to be relatively rare and it's
not necessarily the right tradeoff to spend so much time
serializing/deserializing this data, so this commit offloads the section
into a custom-encoded binary format located elsewhere in the compiled image.

This is similar to #3240 in its goal which is to move very large pieces
of metadata to their own sections to avoid decoding anything when we
load a precompiled modules. This also has a small benefit that it's
slightly more efficient storage for the trap information too, but that's
a negligible benefit.

This is part of #3230 to make loading modules fast.

crates/environ/src/lib.rs

@@ -30,6 +30,7 @@ mod module;
 mod module_environ;
 pub mod obj;
 mod stack_map;
+mod trap_encoding;
 mod tunables;
 mod vmoffsets;
 
@@ -39,6 +40,7 @@ pub use crate::compilation::*;
 pub use crate::module::*;
 pub use crate::module_environ::*;
 pub use crate::stack_map::StackMap;
+pub use crate::trap_encoding::*;
 pub use crate::tunables::Tunables;
 pub use crate::vmoffsets::*;