Refactorings to extract a selected expression into a local function, a module function or a private member

[xperiandri]

Description

Stacked on #20537: this branch contains its commits; the extract-function commits on top of them belong to this PR.

Adds three refactorings (Ctrl+. on a selection) that extract the selected expression into a local function, a module-level function, or a private member — building on the selection/placement logic from #20537. As with Extract to let binding, a caret alone inside the fun <params> -> header of a parenthesized lambda extracts the whole lambda.

Values the selection reads from its enclosing function, member or lambda (but doesn't itself define) become parameters, in the order they're first used; module-level values, other members and this/base stay where they are and aren't parameterized. A member with a named self identifier (member this.M, not member _.M) additionally gets "Extract to private member", called on that identifier; a selection using base offers only that variant (a module or local function can't reach base). Parameter types default to fully annotated (FullType.FormatWithConstraints), since the extracted binding is its own generalization point and would otherwise default surprising types (e.g. int from x * y before the call site is seen) or fail outright on a plain member access; a new Parameter types in Extract to function option under Tools ▸ Options ▸ F# ▸ Code Fixes lets that be relaxed to "only where inference needs it" or "never". The refactoring isn't offered at all when the selection assigns to a captured mutable (the new parameter would only get a copy) or reads a byref/byref-like value from outside the selection.

Covered cases

Offered

• Values the selection uses from the enclosing declaration become parameters of a local function: printfn "%d" (w * h + 1) → let extractedFunction (w: int) (h: int) = w * h + 1 + printfn "%d" (extractedFunction w h)
• The module function is inserted before the declaration that uses it: let private extractedFunction (w: int) (h: int) = w * h + 1 above let area …
• Selecting (w * h + 1) with its parentheses gives the same result, and the call stays parenthesized
• A selection that uses no outside values becomes a function of unit: 1 + 2 → let extractedFunction () = 1 + 2 + extractedFunction ()
• A selection that uses this becomes a private member after the enclosing member: l * this.Rate in List.sumBy (fun l -> l * this.Rate) → this.ExtractedMethod(l) + member private this.ExtractedMethod(l: int) = l * this.Rate
• The parameter-annotation option: Always → let extractedFunction (s: string) (n: int) =, WhenNeeded → (s: string) n (only the receiver of s.ToUpper() is annotated), Never → s n
• Which actions appear: a plain selection (w * h + 1) offers "Extract to local function" and "Extract to module function"; a selection using base (base.ToString() + "!") offers only "Extract to private member"
• A caret in the header of a parenthesized lambda (x -> in (fun x -> x + n)) offers the same actions, with the same results, as selecting the whole (fun x -> x + n)

Not offered

• With no selection, a caret in the lambda body: x + n in (fun x -> x + n)
• The selection assigns to a captured mutable local: for i in 1 .. 3 do n <- n + i
• The selection reads a byref parameter: x + 1 with x: byref<int>

Relates to #14449 (extract method).

Checklist

• Test cases added
• Performance benchmarks added in case of performance changes (not applicable)
• Release notes entry updated

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✅ Found changes and release notes in following paths:

Change path	Release notes path	Description
`vsintegration/src`	docs/release-notes/.VisualStudio/18.vNext.md

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