[RFC FS-1102] Discussion thread for discards on use bindings

[Happypig375]

RFC: https://github.com/fsharp/fslang-design/blob/master/RFCs/FS-1102-discards-on-use-bindings.md
Suggestion: fsharp/fslang-suggestions#881

[charlesroddie]

This RFC doesn't match fsharp/fslang-suggestions#881 (underscore in use bindings) but instead is an extension or follow-on suggestion (pattern matches in use bindings). Usually there is some discussion in fslang-suggestions before posting RFCs. fsharp/fslang-suggestions#881 itself doesn't need an RFC as it's very straightforward.

The behaviour in a follow-on suggestion would need to be discussed/specced. This PR says it should match CEs, but also suggests that tuples of IDisposables should be deconstructed, which don't seem to be possible from CEs.

[dsyme]

Yes, this is correct, as spec'd this wasn't approved. The only thing approved is the use of use _ = ....

[dsyme]

My comment here: fsharp/fslang-suggestions#881 (comment)