winch: Adding support for integration tests (#5588)

* Adding in the foundations for Winch `filetests`

This commit adds two new crates into the Winch workspace:
`filetests` and `test-macros`. The intent is to mimic the
structure of Cranelift `filetests`, but in a simpler way.

* Updates to documentation

This commits adds a high level document to outline how to test Winch
through the `winch-tools` utility. It also updates some inline
documentation which gets propagated to the CLI.

* Updating test-macro to use a glob instead of only a flat directory

cranelift/Cargo.toml

@@ -46,6 +46,9 @@ thiserror = { workspace = true }
 walkdir = "2.2"
 anyhow = { workspace = true }
 clap = { workspace = true }
+similar = { workspace = true }
+toml = { workspace = true }
+serde = { workspace = true }
 
 [features]
 default = ["disas", "wasm", "cranelift-codegen/all-arch", "cranelift-codegen/trace-log", "souper-harvest"]