Fix double-space-to-period supppression on macOS Chrome

FIX: Make sure macOS double-space-to-period conversions are properly suppressed.

See https://discuss.codemirror.net/t/dot-being-added-when-pressing-space-repeatedly/3899/13

Author: marijnh

src/domobserver.ts

@@ -553,7 +553,7 @@ class EditContextManager {
       selectionEnd: this.toContextPos(view.state.selection.main.head)
     })
     this.handlers.textupdate = e => {
-      let {anchor} = view.state.selection.main
+      let {anchor, head} = view.state.selection.main
       let from = this.toEditorPos(e.updateRangeStart), to = this.toEditorPos(e.updateRangeEnd)
       if (view.inputState.composing >= 0 && !this.composing)
         this.composing = {contextBase: e.updateRangeStart, editorBase: from, drifted: false}
@@ -565,6 +565,9 @@ class EditContextManager {
 
       // Edit contexts sometimes fire empty changes
       if (change.from == change.to && !change.insert.length) return
+      if ((browser.mac || browser.android) && change.from == head - 1 &&
+          /^\. ?$/.test(e.text) && view.contentDOM.getAttribute("autocorrect") == "off")
+        change = {from, to, insert: Text.of([e.text.replace(".", " ")])}
 
       this.pendingContextChange = change
       if (!view.state.readOnly) {