IDocument: Simplify permission changes

Take care of handling file permission changes centrally.

TextDocument had its own, caching implementation of tracking the backing
file's read-only state. Move that into IDocument directly.

IDocument::reload with a permission-only change is not a very
interesting case, but every subclass needed to add handling of it.
Instead, remove TypePermission from the file-change types, and handle it
separately via the now unified checkPermissions() implementation.
IDocument::reloadBehavior already was never called with TypePermission.

Change-Id: I321d47ba6193bc878efa9bb50ba7a739fa492745
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/coreplugin/idocument.h

@@ -68,7 +68,6 @@ public:
 
     enum ChangeType {
         TypeContents,
-        TypePermissions,
         TypeRemoved
     };
 
@@ -104,7 +103,7 @@ public:
     void setUniqueDisplayName(const QString &name);
     QString uniqueDisplayName() const;
 
-    virtual bool isFileReadOnly() const;
+    bool isFileReadOnly() const;
     bool isTemporary() const;
     void setTemporary(bool temporary);
 
@@ -123,7 +122,7 @@ public:
     virtual ReloadBehavior reloadBehavior(ChangeTrigger state, ChangeType type) const;
     virtual bool reload(QString *errorString, ReloadFlag flag, ChangeType type);
 
-    virtual void checkPermissions();
+    void checkPermissions();
 
     bool autoSave(QString *errorString, const QString &filePath);
     void setRestoredFrom(const QString &name);