Fix all does not apply the fix sequentially

[charlescyt]

Describe the bug
Consider a fix that adds a statement inside the dispose method of a stateful widget. To do so, the fix

1. checks for existing dispose method
2. adds dispose method only if none exists
3. add a statement inside the dispose method

The fix works fine when being applied alone, but adds multiple dispose methods with Fix all.

Expected behavior
Fix all should handle the fix sequentially, and the subsequent fix should respect the changes that the previous fix has made.

[rrousselGit]

That's normal. It would be awfully slow if we were to apply fixes one-by-one. And it's be fairly challenging to differentiate between:

• A fix that didn't quite fix the issue
• A new problem that appeared
• Or an old problem that has yet to be fixed

Instead, your fix should work regardless of whether it is applied once or in bulk (although admittedly, it isn't intuitive or always simple to do)

[rrousselGit]

(we'd probably want some form of fixAll method that we can override to customize bulk-fix more easily)