Allow record fields to implement signature members

[dsyme]

Currently a record type

type R = { X: int }

Can't implement a signature

type R =
    member X: int

This is perfectly legitimate and useful.

Pros and Cons

The advantages of making this adjustment to F# are signatures are more natural

The disadvantages of making this adjustment to F# are cost

Extra information

Estimated cost (XS, S, M, L, XL, XXL): S

Related suggestions: https://github.com/fsharp/fslang-suggestions/issues/1122

Affidavit (please submit!)

Please tick this by placing a cross in the box:

• [x] This is not a question (e.g. like one you might ask on stackoverflow) and I have searched stackoverflow for discussions of this issue
• [x] I have searched both open and closed suggestions on this site and believe this is not a duplicate
• [x] This is not something which has obviously "already been decided" in previous versions of F#. If you're questioning a fundamental design decision that has obviously already been taken (e.g. "Make F# untyped") then please don't submit it.

Please tick all that apply:

• [x] This is not a breaking change to the F# language design
• [x] I or my company would be willing to help implement and/or test this

For Readers

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[dsyme]

There are related questions about whether the record and union patterns (#164, #1152) can be used to implement portions of the corresponding signature patterns.