feature: frontmatter syntax support

[epage]

Did you check the tree-sitter docs?

• [x] I have read all the tree-sitter docs if it relates to using the parser

Is your feature request related to a problem? Please describe.

RFC #3503 adds support for a new frontmatter syntax. The contained content format is defined by the calling tool with a tool identifier.

In RFC #3502, the cargo infostring identifier would be used to signify the block uses the Cargo.toml format/schema. Cargo will assume that an empty infostring is meant to be used with it.

These are not stable. Stabilization is being tracked in:

• https://github.com/rust-lang/rust/issues/136889
• https://github.com/rust-lang/cargo/issues/12207

Describe the solution you'd like

To parse the frontmatter

Describe alternatives you've considered

N/A

Additional context

No response