[clang] [TySan] Add initial documentation for Type Sanitizer (PR #123595)

[Florian Hahn via cfe-commits]

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+================
+TypeSanitizer
+================
+
+.. contents::
+   :local:
+
+Introduction
+============
+
+TypeSanitizer is a detector for strict type aliasing violations. It consists of a compiler
+instrumentation module and a run-time library. The tool detects violations such as the use 
+of an illegally cast pointer, or misuse of a union.
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fhahn wrote:

I think this should say something about accessing memory with a different type than the dynamic type of the object or something like that?

https://github.com/llvm/llvm-project/pull/123595