vim-patch:9.1.1009: diff feature can be improved

Problem:  diff feature can be improved
Solution: include the linematch diff alignment algorithm
          (Jonathon)

closes: vim/vim#9661

7c7a4e6d1a

Co-authored-by: Jonathon <jonathonwhite@protonmail.com>

runtime/lua/vim/_meta/options.lua

@@ -1631,11 +1631,20 @@ vim.go.dex = vim.go.diffexpr
 --- Option settings for diff mode.  It can consist of the following items.
 --- All are optional.  Items must be separated by a comma.
 ---
---- 	filler		Show filler lines, to keep the text
---- 			synchronized with a window that has inserted
---- 			lines at the same position.  Mostly useful
---- 			when windows are side-by-side and 'scrollbind'
---- 			is set.
+--- 	algorithm:{text} Use the specified diff algorithm with the
+--- 			internal diff engine. Currently supported
+--- 			algorithms are:
+--- 			myers      the default algorithm
+--- 			minimal    spend extra time to generate the
+--- 				   smallest possible diff
+--- 			patience   patience diff algorithm
+--- 			histogram  histogram diff algorithm
+---
+--- 	closeoff	When a window is closed where 'diff' is set
+--- 			and there is only one window remaining in the
+--- 			same tab page with 'diff' set, execute
+--- 			`:diffoff` in that window.  This undoes a
+--- 			`:diffsplit` command.
 ---
 --- 	context:{n}	Use a context of {n} lines between a change
 --- 			and a fold that contains unchanged lines.
@@ -1646,6 +1655,23 @@ vim.go.dex = vim.go.diffexpr
 --- 			value (999999) to disable folding completely.
 --- 			See `fold-diff`.
 ---
+--- 	filler		Show filler lines, to keep the text
+--- 			synchronized with a window that has inserted
+--- 			lines at the same position.  Mostly useful
+--- 			when windows are side-by-side and 'scrollbind'
+--- 			is set.
+---
+--- 	foldcolumn:{n}	Set the 'foldcolumn' option to {n} when
+--- 			starting diff mode.  Without this 2 is used.
+---
+--- 	followwrap	Follow the 'wrap' option and leave as it is.
+---
+--- 	horizontal	Start diff mode with horizontal splits (unless
+--- 			explicitly specified otherwise).
+---
+--- 	hiddenoff	Do not use diff mode for a buffer when it
+--- 			becomes hidden.
+---
 --- 	iblank		Ignore changes where lines are all blank.  Adds
 --- 			the "-B" flag to the "diff" command if
 --- 			'diffexpr' is empty.  Check the documentation
@@ -1659,6 +1685,17 @@ vim.go.dex = vim.go.diffexpr
 --- 			are considered the same.  Adds the "-i" flag
 --- 			to the "diff" command if 'diffexpr' is empty.
 ---
+--- 	indent-heuristic
+--- 			Use the indent heuristic for the internal
+--- 			diff library.
+---
+--- 	internal	Use the internal diff library.  This is
+--- 			ignored when 'diffexpr' is set.  *E960*
+--- 			When running out of memory when writing a
+--- 			buffer this item will be ignored for diffs
+--- 			involving that buffer.  Set the 'verbose'
+--- 			option to see when this happens.
+---
 --- 	iwhite		Ignore changes in amount of white space.  Adds
 --- 			the "-b" flag to the "diff" command if
 --- 			'diffexpr' is empty.  Check the documentation
@@ -1678,56 +1715,19 @@ vim.go.dex = vim.go.diffexpr
 --- 			of the "diff" command for what this does
 --- 			exactly.
 ---
---- 	horizontal	Start diff mode with horizontal splits (unless
---- 			explicitly specified otherwise).
+--- 	linematch:{n}   Align and mark changes between the most
+--- 			similar lines between the buffers. When the
+--- 			total number of lines in the diff hunk exceeds
+--- 			{n}, the lines will not be aligned because for
+--- 			very large diff hunks there will be a
+--- 			noticeable lag. A reasonable setting is
+--- 			"linematch:60", as this will enable alignment
+--- 			for a 2 buffer diff hunk of 30 lines each,
+--- 			or a 3 buffer diff hunk of 20 lines each.
 ---
 --- 	vertical	Start diff mode with vertical splits (unless
 --- 			explicitly specified otherwise).
 ---
---- 	closeoff	When a window is closed where 'diff' is set
---- 			and there is only one window remaining in the
---- 			same tab page with 'diff' set, execute
---- 			`:diffoff` in that window.  This undoes a
---- 			`:diffsplit` command.
----
---- 	hiddenoff	Do not use diff mode for a buffer when it
---- 			becomes hidden.
----
---- 	foldcolumn:{n}	Set the 'foldcolumn' option to {n} when
---- 			starting diff mode.  Without this 2 is used.
----
---- 	followwrap	Follow the 'wrap' option and leave as it is.
----
---- 	internal	Use the internal diff library.  This is
---- 			ignored when 'diffexpr' is set.  *E960*
---- 			When running out of memory when writing a
---- 			buffer this item will be ignored for diffs
---- 			involving that buffer.  Set the 'verbose'
---- 			option to see when this happens.
----
---- 	indent-heuristic
---- 			Use the indent heuristic for the internal
---- 			diff library.
----
---- 	linematch:{n}   Enable a second stage diff on each generated
---- 			hunk in order to align lines. When the total
---- 			number of lines in a hunk exceeds {n}, the
---- 			second stage diff will not be performed as
---- 			very large hunks can cause noticeable lag. A
---- 			recommended setting is "linematch:60", as this
---- 			will enable alignment for a 2 buffer diff with
---- 			hunks of up to 30 lines each, or a 3 buffer
---- 			diff with hunks of up to 20 lines each.
----
---- 	algorithm:{text} Use the specified diff algorithm with the
---- 			internal diff engine. Currently supported
---- 			algorithms are:
---- 			myers      the default algorithm
---- 			minimal    spend extra time to generate the
---- 				   smallest possible diff
---- 			patience   patience diff algorithm
---- 			histogram  histogram diff algorithm
----
 --- Examples:
 ---
 --- ```vim