`Trust` defaulted to `Local`, and `DocState::new` set it, so a
document was trusted unless its maker remembered to mark it. Every
current path that reads a file goes through `file.open`, which marks
it `FromFile`, but a later way of building a document from bytes
(recovery, templates, a new import) would have come out trusted by
omission.
`DocState::new` now takes the `Trust`, and `Trust` has no default.
New workbooks and samples pass `Local`, `file.open` passes
`FromFile`, a new window passes the trust of its workbook, and the
tests that build documents from bytes pass `FromFile`.