[clang] Make lifetimebound and GSL analysis more coherent (#105884)

This allows clang to detect more use-after-free bugs (shown in the
#100549).

This relands the remaining change (removing the EnableLifetimeWarnings
flag) in #104906, with a proper
fix for the regression.

Fixes #100549

Author: hokein

clang/docs/ReleaseNotes.rst

@@ -270,6 +270,9 @@ Improvements to Clang's diagnostics
 
 - Clang now respects lifetimebound attribute for the assignment operator parameter. (#GH106372).
 
+- The lifetimebound and GSL analysis in clang are coherent, allowing clang to
+  detect more use-after-free bugs. (#GH100549).
+
 Improvements to Clang's time-trace
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