Jackson 3 series companion code

37 runnable examples covering the eight feature posts on ankurm.com, verified
against Jackson 3.2.1 on Temurin 21.0.5. Every output committed under docs/ was
produced by run-all.sh.

Also documents 11 places where the published snippets do not compile or do not
behave as printed against a real Jackson 3 build - most notably that
writeValueAsString(List<Base>) silently drops the polymorphic type discriminator,
so the post's serialised output cannot be read back.

docs/output/H02DefaultTypingRemoved.txt

@@ -0,0 +1,14 @@
+--- tools.jackson.databind.ObjectMapper ---
+  enableDefaultTyping              ABSENT
+  activateDefaultTyping            ABSENT
+  setSerializationInclusion        ABSENT
+  registerModule                   ABSENT
+  addMixIn                         ABSENT
+total set*() mutators: 0
+
+--- tools.jackson.databind.json.JsonMapper.Builder ---
+  activateDefaultTyping            present
+  deactivateDefaultTyping          present
+  polymorphicTypeValidator         present
+  changeDefaultPropertyInclusion   present
+  serializationInclusion           ABSENT