vim-patch:8.2.4724: current instance of last search pattern not easily spotted

Problem:    Current instance of last search pattern not easily spotted.
Solution:   Add CurSearch highlighting. (closes vim/vim#10133)

a43993897a

Some code is superseded by later patches that are already ported.

Co-authored-by: LemonBoy <thatlemon@gmail.com>

runtime/doc/news.txt

@@ -47,6 +47,8 @@ EDITOR
 
 • The order in which signs are placed was changed. Higher priority signs will
   now appear left of lower priority signs.
+• |hl-CurSearch| now behaves the same as Vim and no longer updates on every
+  cursor movement.
 
 EVENTS
 

runtime/doc/syntax.txt

@@ -4969,8 +4969,9 @@ ColorColumn	Used for the columns set with 'colorcolumn'.
 Conceal		Placeholder characters substituted for concealed
 		text (see 'conceallevel').
 							*hl-CurSearch*
-CurSearch	Used for highlighting a search pattern under the cursor
-		(see 'hlsearch').
+CurSearch	Current match for the last search pattern (see 'hlsearch').
+		Note: This is correct after a search, but may get outdated if
+		changes are made or the screen is redrawn.
 						*hl-Cursor* *hl-lCursor*
 Cursor		Character under the cursor.
 lCursor		Character under the cursor when |language-mapping|

runtime/doc/vim_diff.txt

@@ -539,8 +539,6 @@ Functions:
 Highlight groups:
 - |hl-ColorColumn|, |hl-CursorColumn| are lower priority than most other
   groups
-- |hl-CurSearch| highlights match under cursor instead of last match found
-  using |n| or |N|
 - |hl-CursorLine| is low-priority unless foreground color is set
 - |hl-VertSplit| superseded by |hl-WinSeparator|
 - Highlight groups names are allowed to contain `@` characters.