[server] new request API

src/plugins/server/data.ml

src/plugins/server/doc.ml

src/plugins/server/doc.mli

src/plugins/server/kernel_ast.ml

src/plugins/server/kernel_fc.ml

src/plugins/server/kernel_project.ml

src/plugins/server/request.ml

src/plugins/server/request.mli

src/plugins/server/syntax.ml

src/plugins/server/syntax.mli