BRIN: mask BRIN_EVACUATE_PAGE for WAL consistency checking

That bit is unlogged and therefore it's wrong to consider it in WAL page
comparison.

Add a test that tickles the case, as branch testing technology allows.

This has been a problem ever since wal consistency checking was
introduced (commit a507b86900 for pg10), so backpatch to all supported
branches.

Author: 王海洋 (Haiyang Wang) <wanghaiyang.001@bytedance.com>
Reviewed-by: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Discussion: https://postgr.es/m/CACciXAD2UvLMOhc4jX9VvOKt7DtYLr3OYRBhvOZ-jRxtzc_7Jg@mail.gmail.com
Discussion: https://postgr.es/m/CACciXADOfErX9Bx0nzE_SkdfXr6Bbpo5R=v_B6MUTEYW4ya+cg@mail.gmail.com

src/backend/access/brin/brin_pageops.c

@@ -541,7 +541,12 @@ brin_start_evacuating_page(Relation idxRel, Buffer buf)
 		lp = PageGetItemId(page, off);
 		if (ItemIdIsUsed(lp))
 		{
-			/* prevent other backends from adding more stuff to this page */
+			/*
+			 * Prevent other backends from adding more stuff to this page:
+			 * BRIN_EVACUATE_PAGE informs br_page_get_freespace that this page
+			 * can no longer be used to add new tuples.  Note that this flag
+			 * is not WAL-logged, except accidentally.
+			 */
 			BrinPageFlags(page) |= BRIN_EVACUATE_PAGE;
 			MarkBufferDirtyHint(buf, true);
 

src/backend/access/brin/brin_xlog.c

@@ -358,4 +358,10 @@ brin_mask(char *pagedata, BlockNumber blkno)
 	{
 		mask_unused_space(page);
 	}
+
+	/*
+	 * BRIN_EVACUATE_PAGE is not WAL-logged, since it's of no use in recovery.
+	 * Mask it.  See brin_start_evacuating_page() for details.
+	 */
+	BrinPageFlags(page) &= ~BRIN_EVACUATE_PAGE;
 }