Refactor reloption handling for index AMs in-core

This reworks the reloption parsing and build of a couple of index AMs by
creating new structures for each index AM's options.  This split was
already done for BRIN, GIN and GiST (which actually has a fillfactor
parameter), but not for hash, B-tree and SPGiST which relied on
StdRdOptions due to an overlap with the default option set.

This saves a couple of bytes for rd_options in each relcache entry with
indexes making use of relation options, and brings more consistency
between all index AMs.  While on it, add a couple of AssertMacro() calls
to make sure that utility macros to grab values of reloptions are used
with the expected index AM.

Author: Nikolay Shaplov
Reviewed-by: Amit Langote, Michael Paquier, Álvaro Herrera, Dent John
Discussion: https://postgr.es/m/4127670.gFlpRb6XCm@x200m

src/tools/pgindent/typedefs.list

@@ -171,6 +171,7 @@ BTInsertStateData
 BTLeader
 BTMetaPageData
 BTOneVacInfo
+BTOptions
 BTPS_State
 BTPageOpaque
 BTPageOpaqueData
@@ -978,6 +979,7 @@ HashJoinTuple
 HashMemoryChunk
 HashMetaPage
 HashMetaPageData
+HashOptions
 HashPageOpaque
 HashPageOpaqueData
 HashPageStat
@@ -2270,6 +2272,7 @@ SpGistLeafTupleData
 SpGistMetaPageData
 SpGistNodeTuple
 SpGistNodeTupleData
+SpGistOptions
 SpGistPageOpaque
 SpGistPageOpaqueData
 SpGistScanOpaque