Snippet index: implement codegen foundations (#8383)

All the codegen to generate the autogenerated parts of the new snippet
index.


[Rendered](https://github.com/rerun-io/rerun/blob/cmc/snippets_index_1_autogen/docs/snippets/INDEX.md)

* Fixes #1123
* Fixes #5662
* DNM: requires #8382

Generated data can be re-used for:
* #2934

crates/build/re_types_builder/src/bin/build_re_types.rs

@@ -21,6 +21,7 @@ const CPP_OUTPUT_DIR_PATH: &str = "rerun_cpp";
 const PYTHON_OUTPUT_DIR_PATH: &str = "rerun_py/rerun_sdk/rerun";
 const PYTHON_TESTING_OUTPUT_DIR_PATH: &str = "rerun_py/tests/test_types";
 const DOCS_CONTENT_DIR_PATH: &str = "docs/content/reference/types";
+const SNIPPETS_REF_DIR_PATH: &str = "docs/snippets/";
 
 /// This uses [`rayon::scope`] to spawn all closures as tasks
 /// running in parallel. It blocks until all tasks are done.
@@ -91,6 +92,7 @@ fn main() {
     let python_output_dir_path = workspace_dir.join(PYTHON_OUTPUT_DIR_PATH);
     let python_testing_output_dir_path = workspace_dir.join(PYTHON_TESTING_OUTPUT_DIR_PATH);
     let docs_content_dir_path = workspace_dir.join(DOCS_CONTENT_DIR_PATH);
+    let snippets_ref_dir_path = workspace_dir.join(SNIPPETS_REF_DIR_PATH);
 
     let cur_hash = read_versioning_hash(&re_types_source_hash_path);
     re_log::debug!("cur_hash: {cur_hash:?}");
@@ -159,6 +161,13 @@ fn main() {
             &arrow_registry,
             check,
         ),
+        || re_types_builder::generate_snippets_ref(
+            &reporter,
+            snippets_ref_dir_path,
+            &objects,
+            &arrow_registry,
+            check,
+        ),
     );
 
     report.finalize();

crates/build/re_types_builder/src/codegen/docs/mod.rs

@@ -1,4 +1,5 @@
 mod arrow_datatype;
+mod snippets_ref;
 mod website;
 
-pub use self::website::DocsCodeGenerator;
+pub use self::{snippets_ref::SnippetsRefCodeGenerator, website::DocsCodeGenerator};