Part of #4936: custom dictionary and Ignore All commands

text.spelling.addWord, removeWord and changeWord are Check Spelling's Add
and Edit Custom Dictionary's Add, Delete and Change; text.spelling.dictionary
lists the words. They live in craft-proof, which every language's check
reads. The desktop app and vectorcraft-cli keep them in
`Custom Dictionary.txt` next to the preferences (none without preferences);
elsewhere they last until the app closes.

text.spelling.ignoreAll is Ignore All: the active document's checks skip the
word while it is open; not saved, not undoable, and not a change to the
document's revision.

Behaviour: https://helpx.adobe.com/illustrator/desktop/design-with-text/edit-format-text/check-and-correct-spelling.html

crates/engine/src/session/documents.rs

@@ -80,6 +80,7 @@ impl Session {
             brush_libraries: Default::default(),
             libraries: Default::default(),
             pdf_preset_dir: None,
+            dictionary_file: None,
             profile_dir: None,
             plugin_dir: None,
             ignored_plugin_grants: Default::default(),