Rename dialog doesn't warn about conflicts new name will introduce

[olegtk]

Version Used: Channel: Canary
Version: 18.3.0 Insiders [11302.173.main]

Steps to Reproduce:

1. Create a C# class with methods Foo and Bar
2. Invoke Rename on Foo and type "Bar"

Expected Behavior:
Rename dialog should warn me about conflict with existing Bar method

Actual Behavior:
No warning in the dialog, but Bar gets some sort of red adornment and squiggle. But if it's out of view port I have no way of knowing.