[clang] [Doc] Update documentation for no-transitive-change (PR #96453)

[Ilya Biryukov via cfe-commits]

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@@ -652,6 +652,134 @@ in the future. The expected roadmap for Reduced BMIs as of Clang 19.x is:
    comes, the term BMI will refer to the Reduced BMI and the Full BMI will only
    be meaningful to build systems which elect to support two-phase compilation.
 
+Experimental No Transitive Change
+---------------------------------
+
+Starting with clang19.x, we introduced an experimental feature: the non-transitive
+change for modules, aimed at reducing unnecessary recompilations. For example,
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ilya-biryukov wrote:

Yeah, I meant the example we already have. The current state LG, resolving this thread.

https://github.com/llvm/llvm-project/pull/96453