Introduce optional global TypeInfoCache

In the current implementation, `TypeInfoCache` is a per-connection
cache. This means, over time, that the same type information is
retrieved from the database copious times. For some DB systems, this
has a negative cost/performance impact.

Introduce an optional global `TypeInfoCache`. This is useful for
cases where a single DB system is used in Production for all
connections and there's no need for each connection to re-retrieve
type info.

- Extract the storage portion of `TypeInfoCache` into a new class,
`TypeInfoCacheStorage`
- Add new property, `GLOBAL_TYPE_INFO_CACHE` to enable a global cache
- When enabled, the constant `TypeInfoCacheStorage GLOBAL_INSTANCE` is
always used. Over the course of running a Production instance, this global
cache should not need to query the database for type info.

pgjdbc/src/main/java/org/postgresql/PGProperty.java

@@ -237,6 +237,14 @@ public enum PGProperty {
           + "the statements reaches the same connection that is being initialized."
   ),
 
+  GLOBAL_TYPE_INFO_CACHE(
+      "globalTypeInfoCache",
+      "false",
+      "Use a type info cache that is global to the driver and not to each connection. "
+          + "This can improve overall performance over time by limiting queries to the database "
+          + "to get type metadata."
+  ),
+
   GSS_ENC_MODE(
       "gssEncMode",
       "allow",

pgjdbc/src/main/java/org/postgresql/jdbc/PgConnection.java

@@ -349,7 +349,9 @@ public PgConnection(HostSpec[] hostSpecs,
 
     // Initialize object handling
     @SuppressWarnings("argument")
-    TypeInfo typeCache = createTypeInfo(this, unknownLength);
+    TypeInfo typeCache = PGProperty.GLOBAL_TYPE_INFO_CACHE.getBoolean(info)
+        ? new TypeInfoCache(this, unknownLength, TypeInfoCacheStorage.GLOBAL_INSTANCE)
+        : createTypeInfo(this, unknownLength);
     this.typeCache = typeCache;
     initObjectTypes(info);