Add a refactoring between namespace + nested module and root module

[xperiandri]

Offers Ctrl+. on the header to turn namespace A.B with a single nested module C = into module A.B.C, and back. opens before the nested module move under the new header; the body is re-indented line by line, leaving multi-line strings alone.

Not offered when the namespace holds anything besides leading opens and the module, or when the file has a paired .fsi (the signature would stop matching, FS0240).

🤖 Generated with Claude Code

[github-actions]

❗ Release notes required

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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

[github-actions]

🔍 Tooling Safety Check — Affects-Design-Time
Affects-Design-Time: Modifies Visual Studio code executed while projects are open.

Generated by PR Tooling Safety Check · gpt56 1.8M · ◷

[T-Gro]

🤖🕵️ Please shorten the description using this guidance. Focus on the problem and why the change is needed, in simplified technical English. Leave the implementation inventory to the Files tab and retain necessary caveats.

[xperiandri]

Covered cases

Converts

• namespace My.Company + module private Helpers = ⟷ module private My.Company.Helpers, both directions, with the caret on the namespace or the module line; covers an XML doc comment, [<AutoOpen; RequireQualifiedAccess>], let inline and a multi-line triple-quoted string whose lines are not re-indented
• rec on the namespace, the module or both: namespace rec A.B / module rec C = → module rec A.B.C
• A comment or XML doc comment before the nested module stays in front of the new header: // Helpers for B. above module A.B.C
• #if DEBUG / #endif inside the body are dedented along with it
• opens between the namespace and the module move below the new header: namespace A.B + open System + module C = → module A.B.C followed by open System; also with several opens, a doc comment on the module, and a comment above the opens (it stays above the header and the opens are not left behind)
• module A.B.C → namespace A.B + module C = with the body indented and blank lines left empty
• module rec A.B.C → module rec C =; header attributes and accessibility are kept: module [<AutoOpen>] internal A.B.C → module [<AutoOpen>] internal C =
• Backticked namespace and a trailing header comment: module ``A-B``.C // header → namespace ``A-B`` + module C = // header
• CRLF kept in both directions: namespace A.B\r\n\r\nmodule C =\r\n let x = 1\r\n ⟷ module A.B.C\r\nlet x = 1\r\n
• Round trip: module A.B.C converted to a nested module and back gives the original text

Not offered

• The namespace holds more than one module (module C = … module D =) or no module (type T = int)
• namespace global with a nested module
• A single-segment root module: module C
• A module written as module C = begin … end
• A comment after the namespace name: namespace A.B // B
• Caret outside the header lines, e.g. on let x = 1, in either shape
• An empty nested module: module C = with no declarations
• An open after the module, or a declaration other than open before it (type T = int)
• The implementation file has a signature file