cranelift-isle: Rewrite error reporting (#5318)

There were several issues with ISLE's existing error reporting
implementation.

- When using Miette for more readable error reports, it would panic if
  errors were reported from multiple files in the same run.
- Miette is pretty heavy-weight for what we're doing, with a lot of
  dependencies.
- The `Error::Errors` enum variant led to normalization steps in many
  places, to avoid using that variant to represent a single error.

This commit:
- replaces Miette with codespan-reporting
- gets rid of a bunch of cargo-vet exemptions
- replaces the `Error::Errors` variant with a new `Errors` type
- removes source info from `Error` variants so they're easy to construct
- adds source info only when formatting `Errors`
- formats `Errors` with a custom `Debug` impl
- shares common code between ISLE's callers, islec and cranelift-codegen
- includes a source snippet even with fancy-errors disabled

I tried to make this a series of smaller commits but I couldn't find any
good split points; everything was too entangled with everything else.

cranelift/isle/isle/Cargo.toml

@@ -9,8 +9,8 @@ repository = "https://github.com/bytecodealliance/wasmtime/tree/main/cranelift/i
 version = "0.91.0"
 
 [dependencies]
+codespan-reporting = { version = "0.11.1", optional = true }
 log = { workspace = true, optional = true }
-miette = { version = "5.1.0", optional = true }
 
 [dev-dependencies]
 tempfile = "3"
@@ -19,4 +19,4 @@ tempfile = "3"
 default = []
 
 logging = ["log"]
-miette-errors = ["miette"]
+fancy-errors = ["codespan-reporting"]