Clarify browser_compat section content handling vs Yari behavior

Context

A content field was added to the Compat struct early on (2024-05-19), allowing browser_compat sections to contain content. However, prose content before a compat marker is intentionally split into a separate section to match Yari's behavior.

The original TODO noted this with "?!" — suggesting it was an observation about Yari's quirky behavior rather than a clear feature request.

Current behavior

In crates/rari-doc/src/html/sections.rs, when prose exists before a compat section, rari splits them into separate sections. A comment in the code says:

We have already something in body. Yari does something weird so we do that too: We push compat section and put prose after that 🤷.

Question

Should this behavior be preserved as-is (matching Yari), documented, or changed?

References

• crates/rari-doc/src/html/sections.rs (section splitting logic)
• crates/rari-doc/src/pages/json.rs (Compat struct with content field)
• crates/rari-doc/src/pages/build.rs (content serialization)

Start with the section-splitting logic in crates/rari-doc/src/html/sections.rs, then trace the Compat content field through crates/rari-doc/src/pages/json.rs and crates/rari-doc/src/pages/build.rs. Compare the current behavior with the stated Yari behavior. Done means the intended behavior is decided and the relevant implementation or documentation reflects that decision.