[PGPRO-12159] Added pageinspect functions for rum.

This commit adds three functions for low-level exploration
of the index's rum pages:

1) rum_metapage_info() -- is used to examine the information
posted on the meta page (flags: {meta}).
2) rum_page_opaque_info() -- is used to examine information
that is placed in the opaque area of the index page (any
index page).
3) rum_leaf_data_page_items() -- is used to examine the
information that is placed on the leaf pages of the
posting tree (flags: {leaf, data}).

To extract information, all these functions need to pass
the index name and the page number.

Tags: rum

Author: arseny114

Makefile

@@ -9,7 +9,7 @@ OBJS = src/rumsort.o src/rum_ts_utils.o src/rumtsquery.o \
 	src/rumbtree.o src/rumbulk.o src/rumdatapage.o \
 	src/rumentrypage.o src/rumget.o src/ruminsert.o \
 	src/rumscan.o src/rumutil.o src/rumvacuum.o src/rumvalidate.o \
-	src/btree_rum.o src/rum_arr_utils.o $(WIN32RES)
+	src/btree_rum.o src/rum_arr_utils.o src/rum_debug_funcs.o $(WIN32RES)
 
 DATA_updates = rum--1.0--1.1.sql rum--1.1--1.2.sql \
 			   rum--1.2--1.3.sql

rum_init.sql

@@ -1724,3 +1724,41 @@ RETURNS float4
 AS 'MODULE_PATHNAME', 'rum_ts_score_td'
 LANGUAGE C IMMUTABLE STRICT;
 
+/*--------------------RUM debug functions-----------------------*/
+
+CREATE FUNCTION rum_metapage_info(
+    IN rel_name text,
+    IN blk_num int8,
+    OUT pending_head bigint,
+    OUT pending_tail bigint,
+    OUT tail_free_size int4,
+    OUT n_pending_pages bigint,
+    OUT n_pending_tuples bigint,
+    OUT n_total_pages bigint,
+    OUT n_entry_pages bigint,
+    OUT n_data_pages bigint,
+    OUT n_entries bigint,
+    OUT version bigint)
+AS 'MODULE_PATHNAME', 'rum_metapage_info'
+LANGUAGE C STRICT PARALLEL SAFE;
+
+CREATE FUNCTION rum_page_opaque_info(
+    IN rel_name text,
+    IN blk_num int8,
+    OUT leftlink bigint,
+    OUT rightlink bigint,
+    OUT maxoff int4,
+    OUT freespace int4,
+    OUT flags text[])
+AS 'MODULE_PATHNAME', 'rum_page_opaque_info'
+LANGUAGE C STRICT PARALLEL SAFE;
+
+CREATE FUNCTION rum_leaf_data_page_items(
+    IN rel_name text,
+    IN blk_num int8,
+    OUT tuple_id tid,
+    OUT add_info_is_null bool,
+    OUT addInfo varchar)
+RETURNS SETOF record
+AS 'MODULE_PATHNAME', 'rum_leaf_data_page_items'
+LANGUAGE C STRICT PARALLEL SAFE;