Shuffle around the wiggle crates (#1414)

* Shuffle around the wiggle crates

This commit reorganizes the wiggle crates slightly by performing the
following transforms:

* The `crates/wiggle` crate, previously named `wiggle`, was moved to
  `crates/wiggle/crates/macro` and is renamed to `wiggle-macro`.

* The `crates/wiggle/crates/runtime` crate, previously named
  `wiggle-runtime`, was moved to `crates/wiggle` and is renamed to
  `wiggle`.

* The new `wiggle` crate depends on `wiggle-macro` and reexports the macro.

The goal here is that consumers only deal with the `wiggle` crate
itself. No more crates depend on `wiggle-runtime` and all dependencies
are entirely on just the `wiggle` crate.

* Remove the `crates/wiggle/crates` directory

Move everything into `crates/wiggle` directly, like `wasi-common`

* Add wiggle-macro to test-all script

* Fixup a test

crates/wiggle/src/error.rs

@@ -0,0 +1,38 @@
+use crate::Region;
+use thiserror::Error;
+
+#[derive(Debug, Error, PartialEq, Eq)]
+pub enum GuestError {
+    #[error("Invalid flag value {0}")]
+    InvalidFlagValue(&'static str),
+    #[error("Invalid enum value {0}")]
+    InvalidEnumValue(&'static str),
+    #[error("Pointer overflow")]
+    PtrOverflow,
+    #[error("Pointer out of bounds: {0:?}")]
+    PtrOutOfBounds(Region),
+    #[error("Pointer not aligned to {1}: {0:?}")]
+    PtrNotAligned(Region, u32),
+    #[error("Pointer already borrowed: {0:?}")]
+    PtrBorrowed(Region),
+    #[error("Slice length mismatch")]
+    SliceLengthsDiffer,
+    #[error("In func {funcname}:{location}:")]
+    InFunc {
+        funcname: &'static str,
+        location: &'static str,
+        #[source]
+        err: Box<GuestError>,
+    },
+    #[error("In data {typename}.{field}:")]
+    InDataField {
+        typename: String,
+        field: String,
+        #[source]
+        err: Box<GuestError>,
+    },
+    #[error("Invalid UTF-8 encountered: {0:?}")]
+    InvalidUtf8(#[from] ::std::str::Utf8Error),
+    #[error("Int conversion error: {0:?}")]
+    TryFromIntError(#[from] ::std::num::TryFromIntError),
+}