[clang] [LifetimeSafety] Implement multi-level origins (PR #168344)

[Yitzhak Mandelbaum via cfe-commits]

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@@ -155,18 +155,19 @@ class OriginEscapesFact : public Fact {
 
 class UseFact : public Fact {
   const Expr *UseExpr;
-  OriginID OID;
+  // The origins of the expression being used.
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ymand wrote:

super nit: maybe explain the choice of 1 as the default length.

https://github.com/llvm/llvm-project/pull/168344