Add documentation formatting and typing support

[davidwengier]

Adds formatting and typing support for @documentation, using the existing documentation-comment formatter rather than treating the XML body as Razor code. Preserves XML text and source mappings, and honours the brace-placement option.

Builds on #85725. Part of #85414.

Remote builds for net10.0 and netstandard2.0. All 158 VS Code and 166 VS cases pass with analysers enabled, including the full 103-case formatting class in each host, auto-insert and VS on-type coverage. Product and tests are separate commits.

Microsoft Reviewers: Open in CodeFlow

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[davidwengier]

Copilot can't stop running git diff --check which flags mixed leading whitespace, so copilot fixes it, which makes the tests fail, so it put it back in weird ways, like {{"\t"}} etc. I'll fix that manually.

[Copilot]

Copilot review overview

🟢 Approval recommended

The implementation is focused, defensively handles malformed input, and has comprehensive cross-host coverage.

Review effort: Balanced
Findings: None

What changed in this PR

Adds formatting and typing support for Razor @documentation blocks while preserving XML content.

Changes:

• Projects documentation bodies as C# documentation comments for Roslyn formatting.
• Supports brace-placement options and safe malformed-input handling.
• Adds extensive formatting, on-type, and auto-insert coverage.

File	Description
CohostOnTypeFormattingEndpointTest.cs	Verifies XML is not formatted as C#.
CodeDirectiveFormattingTest.cs	Covers formatting, braces, tabs, malformed input, and idempotence.
CohostOnAutoInsertEndpointTest.cs	Prevents unwanted insertions while typing documentation.
RazorFormattingPass.cs	Formats documentation directive brace structure.
CSharpFormattingPass.CSharpDocumentGenerator.cs	Projects XML through Roslyn’s documentation formatter.
FormattingVisitor.cs	Classifies documentation directives correctly.
documentation-directive.md	Documents formatting and brace behavior.

[Copilot]

Warning

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Copilot review overview

Review effort: Lite
Findings: 2 · 2

Open (4)

• The condition has become fairly dense (type checks + directive-kind check + two different… · New
• This file/class is now hosting a very large, directive-specific test suite for @documentation,… · New
• The “existing brace placement is preserved” phrasing could be interpreted as “no whitespace… · New
• Line-ending normalization via repeated .Replace("\r\n", "\n") is duplicated across many tests in… · New

[Copilot]

Copilot review overview

🔵 Needs a closer look

The synthetic line-mapping logic is regression-sensitive, existing review threads remain unresolved, and current checks are still in progress.

Review effort: Balanced
Findings: 2 · 2

Open (4)

• This file/class is now hosting a very large, directive-specific test suite for @documentation,…
• The condition has become fairly dense (type checks + directive-kind check + two different…
• Line-ending normalization via repeated .Replace("\r\n", "\n") is duplicated across many tests in…
• The “existing brace placement is preserved” phrasing could be interpreted as “no whitespace…

The base branch was changed.

[Copilot]

Copilot review overview

🟡 Changes recommended

Warning-bearing documentation blocks bypass brace formatting, and the user-facing option text remains outdated.

Review effort: Balanced
Findings: 1 · 1

Open (2)

• Allow brace formatting for documentation blocks with warnings · New
• Update setting text to mention documentation blocks · New

Resolved since last review (4)

• This file/class is now hosting a very large, directive-specific test suite for @documentation,…
• The condition has become fairly dense (type checks + directive-kind check + two different…
• Line-ending normalization via repeated .Replace("\r\n", "\n") is duplicated across many tests in…
• The “existing brace placement is preserved” phrasing could be interpreted as “no whitespace…

[davidwengier]

@dibarbet for re-review after rebase