Rust enum codegen 1/N (#5291)

### What
* Part of #3384

This implements C-style `enum` support in the codegen, with a full Rust
implementation.

There is no example included, because the Python and C++ codegen is
still emitting an error when attempting to use `enum`, but I have tested
the codegen a bit locally, and the generated code at least _compiles_.

Future PRs:
* Python codegen
* C++ codegen
* Tests
* Converting existing types to `enum`

While working on the PR I also cleaned up some other codegen stuff, but
reviewing everything commit-by-commit should make it all obvious.

### Checklist
* [x] I have read and agree to [Contributor
Guide](https://github.com/rerun-io/rerun/blob/main/CONTRIBUTING.md) and
the [Code of
Conduct](https://github.com/rerun-io/rerun/blob/main/CODE_OF_CONDUCT.md)
* [x] I've included a screenshot or gif (if applicable)
* [x] I have tested the web demo (if applicable):
* Using newly built examples:
[app.rerun.io](https://app.rerun.io/pr/5291/index.html)
* Using examples from latest `main` build:
[app.rerun.io](https://app.rerun.io/pr/5291/index.html?manifest_url=https://app.rerun.io/version/main/examples_manifest.json)
* Using full set of examples from `nightly` build:
[app.rerun.io](https://app.rerun.io/pr/5291/index.html?manifest_url=https://app.rerun.io/version/nightly/examples_manifest.json)
* [x] The PR title and labels are set such as to maximize their
usefulness for the next release's CHANGELOG
* [x] If applicable, add a new check to the [release
checklist](https://github.com/rerun-io/rerun/blob/main/tests/python/release_checklist)!

- [PR Build Summary](https://build.rerun.io/pr/5291)
- [Docs
preview](https://rerun.io/preview/017812cb07a396308b070e411334edcf2a4cf352/docs)
<!--DOCS-PREVIEW-->
- [Examples
preview](https://rerun.io/preview/017812cb07a396308b070e411334edcf2a4cf352/examples)
<!--EXAMPLES-PREVIEW-->
- [Recent benchmark results](https://build.rerun.io/graphs/crates.html)
- [Wasm size tracking](https://build.rerun.io/graphs/sizes.html)

.vscode/launch.json

@@ -132,5 +132,27 @@
             "args": [],
             "cwd": "${workspaceFolder}"
         },
+        {
+            "name": "Debug 'codegen'",
+            "type": "lldb",
+            "request": "launch",
+            "cargo": {
+                "args": [
+                    "build",
+                    "--package=re_types_builder",
+                ],
+                "filter": {
+                    "name": "build_re_types",
+                    "kind": "bin"
+                }
+            },
+            "args": [
+                "--force" // always run codegen, even if hashes hasn't changed
+            ],
+            "cwd": "${workspaceFolder}",
+            "env": {
+                "RAYON_NUM_THREADS": "1" // less confusing debugging experience
+            }
+        },
     ]
 }

crates/re_string_interner/src/lib.rs

@@ -107,6 +107,7 @@ impl AsRef<str> for InternedString {
 
 impl std::ops::Deref for InternedString {
     type Target = str;
+
     #[inline]
     fn deref(&self) -> &str {
         self.as_str()
@@ -249,6 +250,7 @@ macro_rules! declare_new_type {
 
         impl std::ops::Deref for $StructName {
             type Target = str;
+
             #[inline]
             fn deref(&self) -> &str {
                 self.as_str()