[specialized.algorithms.general] Restore the note for potentially-overlapping objects and undefined behavior (cplusplus#7326)

The original note was incorrect and removed (see cplusplus#6157). But it turns out
that _some_ note is still helpful. This PR tries to find the right way to
describe storage reusing and potential subsequent undefined behavior.

Author: frederick-vs-ja

source/algorithms.tex

@@ -11156,6 +11156,15 @@
 are destroyed in an unspecified order
 before allowing the exception to propagate.
 
+\pnum
+\begin{note}
+When new objects are created by
+the algorithms specified in \ref{specialized.algorithms},
+the lifetime ends for any existing objects
+(including potentially-overlapping subobjects \ref{intro.object})
+in storage that is reused \ref{basic.life}.
+\end{note}
+
 \pnum
 Some algorithms specified in \ref{specialized.algorithms}
 make use of the exposition-only function template