Remove all global state from the caching system (#863)

* Remove all global state from the caching system

This commit is a continuation of an effort to remove usages of
`lazy_static!` and similar global state macros which can otherwise be
accomodated with passing objects around. Previously there was a global
cache system initialized per-process, but it was initialized in a bit of
a roundabout way and wasn't actually reachable from the `wasmtime` crate
itself. The changes here remove all global state, refactor many of the
internals in the cache system, and makes configuration possible through
the `wasmtime` crate.

Specifically some changes here are:

* Usage of `lazy_static!` and many `static` items in the cache module
  have all been removed.
* Global `cache_config()`, `worker()`, and `init()` functions have all
  been removed. Instead a `CacheConfig` is a "root object" which
  internally owns its worker and passing around the `CacheConfig` is
  required for cache usage.
* The `wasmtime::Config` structure has grown options to load and parse
  cache files at runtime. Currently only loading files is supported,
  although we can likely eventually support programmatically configuring
  APIs as well.
* Usage of the `spin` crate has been removed and the dependency is removed.
* The internal `errors` field of `CacheConfig` is removed, instead
  changing all relevant methods to return a `Result<()>` instead of
  storing errors internally.
* Tests have all been updated with the new interfaces and APIs.

Functionally no real change is intended here. Usage of the `wasmtime`
CLI, for example, should still enable the cache by default.

* Fix lightbeam compilation

crates/environ/src/lightbeam.rs

@@ -1,14 +1,15 @@
 //! Support for compiling with Lightbeam.
 
 use crate::cache::ModuleCacheDataTupleType;
-use crate::compilation::{Compilation, CompileError, Relocations, Traps};
+use crate::compilation::{Compilation, CompileError, Traps};
 use crate::func_environ::FuncEnvironment;
 use crate::module::Module;
 use crate::module_environ::FunctionBodyData;
 // TODO: Put this in `compilation`
 use crate::address_map::{ModuleAddressMap, ValueLabelsRanges};
 use crate::cranelift::RelocSink;
-use cranelift_codegen::{ir, isa};
+use crate::CacheConfig;
+use cranelift_codegen::isa;
 use cranelift_entity::{PrimaryMap, SecondaryMap};
 use cranelift_wasm::{DefinedFuncIndex, ModuleTranslationState};
 
@@ -25,6 +26,7 @@ impl crate::compilation::Compiler for Lightbeam {
         isa: &dyn isa::TargetIsa,
         // TODO
         generate_debug_info: bool,
+        _cache_config: &CacheConfig,
     ) -> Result<ModuleCacheDataTupleType, CompileError> {
         if generate_debug_info {
             return Err(CompileError::DebugInfoNotSupported);