Add support for fuzzystrmatch and other external extensions

Added support for the fuzzystrmatch extension and for other
external extensions.

Added support for typecasting `::pg_text` to TEXTOID.

Added regression tests.

   modified:   sql/agtype_coercions.sql
   modified:   src/backend/parser/cypher_expr.c
   modified:   src/backend/utils/adt/agtype.c
   modified:   regress/expected/expr.out
   modified:   regress/sql/expr.sql

regress/expected/expr.out

@@ -8767,9 +8767,38 @@ SELECT * FROM cypher('issue_1988', $$
  {"id": 844424930131969, "label": "Part", "properties": {"set": "set", "match": "match", "merge": "merge", "create": "create", "delete": "delete", "part_num": 123}}::vertex
 (4 rows)
 
+--
+-- Test external extension function logic for fuzzystrmatch
+--
+SELECT * FROM create_graph('fuzzystrmatch');
+NOTICE:  graph "fuzzystrmatch" has been created
+ create_graph 
+--------------
+
+(1 row)
+
+-- These should fail with extension not installed
+SELECT * FROM cypher('fuzzystrmatch', $$ RETURN soundex("hello world!") $$) AS (result agtype);
+ERROR:  extension fuzzystrmatch is not installed for function soundex
+LINE 1: SELECT * FROM cypher('fuzzystrmatch', $$ RETURN soundex("hel...
+                                               ^
+SELECT * FROM cypher('fuzzystrmatch', $$ RETURN difference("hello world!", "hello world!") $$) AS (result agtype);
+ERROR:  extension fuzzystrmatch is not installed for function difference
+LINE 1: SELECT * FROM cypher('fuzzystrmatch', $$ RETURN difference("...
+                                               ^
 --
 -- Cleanup
 --
+SELECT * FROM drop_graph('fuzzystrmatch', true);
+NOTICE:  drop cascades to 2 other objects
+DETAIL:  drop cascades to table fuzzystrmatch._ag_label_vertex
+drop cascades to table fuzzystrmatch._ag_label_edge
+NOTICE:  graph "fuzzystrmatch" has been dropped
+ drop_graph 
+------------
+
+(1 row)
+
 SELECT * FROM drop_graph('issue_1988', true);
 NOTICE:  drop cascades to 4 other objects
 DETAIL:  drop cascades to table issue_1988._ag_label_vertex

regress/sql/expr.sql

@@ -3536,9 +3536,18 @@ SELECT * FROM cypher('issue_1988', $$
 SELECT * FROM cypher('issue_1988', $$
     MATCH (p) RETURN p $$) as (p agtype);
 
+--
+-- Test external extension function logic for fuzzystrmatch
+--
+SELECT * FROM create_graph('fuzzystrmatch');
+-- These should fail with extension not installed
+SELECT * FROM cypher('fuzzystrmatch', $$ RETURN soundex("hello world!") $$) AS (result agtype);
+SELECT * FROM cypher('fuzzystrmatch', $$ RETURN difference("hello world!", "hello world!") $$) AS (result agtype);
+
 --
 -- Cleanup
 --
+SELECT * FROM drop_graph('fuzzystrmatch', true);
 SELECT * FROM drop_graph('issue_1988', true);
 SELECT * FROM drop_graph('issue_1953', true);
 SELECT * FROM drop_graph('expanded_map', true);

sql/agtype_coercions.sql

@@ -32,6 +32,15 @@ AS 'MODULE_PATHNAME';
 CREATE CAST (agtype AS text)
     WITH FUNCTION ag_catalog.agtype_to_text(agtype);
 
+-- text -> agtype
+CREATE FUNCTION ag_catalog.text_to_agtype(text)
+    RETURNS agtype
+    LANGUAGE c
+    IMMUTABLE
+RETURNS NULL ON NULL INPUT
+PARALLEL SAFE
+AS 'MODULE_PATHNAME';
+
 -- agtype -> boolean (implicit)
 CREATE FUNCTION ag_catalog.agtype_to_bool(agtype)
     RETURNS boolean
@@ -69,7 +78,7 @@ AS 'MODULE_PATHNAME';
 CREATE CAST (float8 AS agtype)
     WITH FUNCTION ag_catalog.float8_to_agtype(float8);
 
--- agtype -> float8 (implicit)
+-- agtype -> float8 (exmplicit)
 CREATE FUNCTION ag_catalog.agtype_to_float8(agtype)
     RETURNS float8
     LANGUAGE c
@@ -106,6 +115,18 @@ CREATE CAST (agtype AS bigint)
     WITH FUNCTION ag_catalog.agtype_to_int8(variadic "any")
 AS ASSIGNMENT;
 
+-- int4 -> agtype (explicit)
+CREATE FUNCTION ag_catalog.int4_to_agtype(int4)
+    RETURNS agtype
+    LANGUAGE c
+    IMMUTABLE
+RETURNS NULL ON NULL INPUT
+PARALLEL SAFE
+AS 'MODULE_PATHNAME';
+
+CREATE CAST (int4 AS agtype)
+    WITH FUNCTION ag_catalog.int4_to_agtype(int4);
+
 -- agtype -> int4
 CREATE FUNCTION ag_catalog.agtype_to_int4(variadic "any")
     RETURNS int
@@ -151,4 +172,4 @@ PARALLEL SAFE
 AS 'MODULE_PATHNAME';
 
 CREATE CAST (agtype AS json)
-    WITH FUNCTION ag_catalog.agtype_to_json(agtype);
+    WITH FUNCTION ag_catalog.agtype_to_json(agtype);