Fading option is not activated on already opened files

[raffaeler]

Version Used:
VS2022 17.14.0 Preview 1

This bug is related to the highlighted option which fades out the unused members:

Steps to Reproduce:

1. Ensure the Fade out unused members is turned on (default)
2. Open a project and at least one C# file that has unused members. Ensure the unused members are fade out
3. Turn off the Fade out unused members
4. The unused members are still fade out
5. Close the file with unused members
6. Reopen the file with unused members
7. Now the unused members are not fade out anymore

Expected Behavior:
I expect that Fade out unused members goes active on the files that are currently open in the editor.

Actual Behavior:
As for the repro, the files that are already open are not fade out.

Reference: #76396 (comment)

[CyrusNajmabadi]

@dibarbet is there a place in Pull Diagnostics where we listen to options changes and use that to issue a diagnostics refresh?