feat(doc): support transient storage keyword

[duelinggalois]

Component

Forge

Describe the feature you would like

For code

    bool private transient varName;

you see the following

-<%>- forge doc --build
Error: Failed to parse Solidity code for path/File.sol
Debug info: [Diagnostic { loc: File(0, 2128, 2135), level: Error, ty: ParserError, message: "unrecognised token 'varName', expected \";\", \"=\"", notes: [] }]

Additional context

No response

[grandizzy]

thank you. same as #9088 but for docs

[duelinggalois]

Closing since its covered in #9088