This is exclusively for the benefit of rust-analyzer, which
sends publishDiagnostics for all project files upfront, and
never republishes them on 'didOpen'.
See https://github.com/joaotavora/eglot/issues/1531.
* lisp/progmodes/eglot.el (eglot--flymake-handle-push): Simplify.
Don't flymake-list-only-diagnostics here.
Save original diagnostic in flymake-list-only-diagnostics setting.
(eglot--on-shutdown): Cleanup flymake-list-only-diagnostics.
(eglot--flymake-report-push+pulled): Hack in data from
flymake-list-only-diagnostics.