Fix significant bug with storing composed matchers

Given that in the 2 or so years that matchers are thing nobody complained,
it seems that people do not actually write this sort of code, and the
possibility will be removed in v3. However, to avoid correctness bugs,
we will have to support this weird code in v2.

projects/SelfTest/Baselines/junit.sw.approved.txt

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <testsuitesloose text artifact
 >
-  <testsuite name="<exe-name>" errors="17" failures="132" tests="1682" hostname="tbd" time="{duration}" timestamp="{iso8601-timestamp}">
+  <testsuite name="<exe-name>" errors="17" failures="132" tests="1684" hostname="tbd" time="{duration}" timestamp="{iso8601-timestamp}">
     <properties>
       <property name="filters" value="~[!nonportable]~[!benchmark]~[approvals]"/>
       <property name="random-seed" value="1"/>
@@ -356,6 +356,7 @@ Exception.tests.cpp:<line number>
     <testcase classname="<exe-name>.global" name="Comparisons between ints where one side is computed" time="{duration}"/>
     <testcase classname="<exe-name>.global" name="Comparisons between unsigned ints and negative signed ints match c++ standard behaviour" time="{duration}"/>
     <testcase classname="<exe-name>.global" name="Comparisons with int literals don't warn when mixing signed/ unsigned" time="{duration}"/>
+    <testcase classname="<exe-name>.global" name="Composed matchers are distinct" time="{duration}"/>
     <testcase classname="<exe-name>.global" name="Contains string matcher" time="{duration}">
       <failure message="testStringForMatching(), Contains(&quot;not there&quot;, Catch::CaseSensitive::No)" type="CHECK_THAT">
 FAILED: