update logo schema for `{path, alt}` object form, Typst

[gordonwoodhull]

From internal discussion

I didn't implement a schema for logo. All formats support object of path and alt as an alternative to the string form for path (which is either a path or a brand.logo name).

Typst additionally supports location, width, padding*

Currently the schema has logo only for dashboard and only as a path.

I don't think we can currently have extra fields for one format, so the schema should only include path and alt and leave the object open.

Test using autocomplete in VSCode.

Ref: #12171

[gordonwoodhull]

This is only complicated because there is a proliferation of definitions of logo, and Typst is piggy-backing on the Reveal one.

Since I'll be revamping logo for dark brand in 1.8, I'm going to put this off.