[Context] Read the API context and the UI application from the Revit 2027 internals

[Nice3point]

Summary of the Pull Request

What is this about:

RevitContext reads the API context and the UI application from internal members of the Revit 2027 API.

Description:

What changed

• On Revit 2027, IsRevitInApiMode calls the internal Application.IsInAPIContext() through an UnsafeAccessor.
• On earlier versions, IsRevitInApiMode calls the native APICallDepthManager functions of RevitDBAPI through function pointers. It no longer invokes them through reflection or loads APIUIAPI.
• On Revit 2027, UiApplication is the session UIApplication from the internal UIApplication.Instance. Earlier versions construct it from Application.
• The runtime project allows unsafe code for the function-pointer calls.

Where to look

• APIUIAPI and RevitDBAPI both declare APICallDepthManager.singletonfactory and isRevitInAPIMode as P/Invoke into the same native functions, in Revit 2023 to 2027.
• UIApplication.Instance returns UIApplication::getInstance(). The public constructor resolves the same native object through getUIApplication(getMFCApp(...)) and rejects a call while a DB application is active.
• Revit keeps the DialogBoxShowing handlers in a static map keyed by the native pointer, so BeginDialogSuppressionScope subscribes and unsubscribes through any wrapper of the session.

How verified

• Build: Release.R20, Release.R24, Release.R26, Release.R27, zero errors.
• Revit tests: 73 passed, zero failed, on Revit 2027 and 2024. Revit 2024 covers the function-pointer path on .NET Framework.
• New tests: IsRevitInApiMode returns false from a thread pool thread, and on the Revit thread for work queued through the dispatcher outside the API context. The second test fails for an implementation that compares threads.
• Revit 2027, measured with BenchmarkDotNet in a Revit process without the user interface:

IsRevitInApiMode implementation	Mean	Allocated
Reflection	61.96 ns	112 B
Function pointers	36.34 ns	—
Application.IsInAPIContext()	27.43 ns	—

• Revit 2026: the installed patch runs on .NET 10, and the committed test project targets .NET 8 for that version. The tests passed only with a temporary .NET 10 target override, before the UiApplication change.

Quality Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• My changes generate no new warnings

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