Catch exceptions from StringMakers inside Detail::stringify

This stops tests failing falsely if the assertion passed, but the
stringification itself failed as the assertion was sent to the reporter.

I don't think that stringification should be fallible, but the
overhead in compilation ended up being small enough (<0.5% on `SelfTest`)
that it might be worth implementing, in case there is more users
with weird `StringMaker`s than just MongoDB.

Closes #2980

tests/SelfTest/Baselines/sonarqube.sw.multi.approved.txt

@@ -387,6 +387,7 @@ at AssertionHandler.tests.cpp:<line number>
   <file path="tests/<exe-name>/IntrospectiveTests/ToString.tests.cpp">
     <testCase name="Directly creating an EnumInfo" duration="{duration}"/>
     <testCase name="Range type with sentinel" duration="{duration}"/>
+    <testCase name="Stringifying bla bla bla" duration="{duration}"/>
     <testCase name="Stringifying char arrays with statically known sizes - char" duration="{duration}"/>
     <testCase name="Stringifying char arrays with statically known sizes - signed char" duration="{duration}"/>
     <testCase name="Stringifying char arrays with statically known sizes - unsigned char" duration="{duration}"/>