"Find references" and rename does not work for F# exceptions

[majocha]

Given a symbol:

exception MyCustomException of string

Neither Ionide nor Visual Studio can find a reference to it or rename it.

[majocha]

The bug is somewhere in ItemKeyStore which looks seriously optimized 😨. Item.ExnCase gets written by the buider, but later is not found.

[majocha]

Well, this is interesting:

The item is an ExnCase when written, but an UnqualifiedType when wa want to find it:

[majocha]

Commenting out this line

fsharp/src/Compiler/Service/ItemKey.fs

Line 469 in 8b7bf60

writeString ItemKeyTags.itemExnCase

fixes it but it's just a workaround.
because Item info for ExnCase is being erased in FSharpEntity constructor.