backport feat(treesitter): expand selection to sibling node (#39323)

Problem:
Can't expand treesitter-incremental-selection to the next and previous
sibling nodes.

Solution:
Pressing `]N` in visual mode will expand the selection to the next
sibling node, and `[N` will do the same with the previous node.

Co-authored-by: altermo <107814000+altermo@users.noreply.github.com>

test/functional/treesitter/select_spec.lua

@@ -64,6 +64,16 @@ describe('treesitter incremental-selection', function()
 
     treeselect('select_parent')
     eq('foo(1)\nbar(2)\n', get_selected())
+
+    set_lines('quux(1,foo,bar,baz,qux,2)')
+    feed('<esc>fbve')
+    eq('bar', get_selected())
+
+    treeselect('select_grow_next')
+    eq('bar,baz', get_selected())
+
+    treeselect('select_grow_prev')
+    eq('foo,bar,baz', get_selected())
   end)
 
   it('repeat', function()
@@ -89,6 +99,14 @@ describe('treesitter incremental-selection', function()
 
     treeselect('select_child', 2)
     eq('2', get_selected())
+
+    feed('<esc>F1')
+    treeselect('select_grow_next', 2)
+    eq('1,2,3', get_selected())
+
+    feed('<esc>f4v')
+    treeselect('select_grow_prev', 2)
+    eq('2,3,4', get_selected())
   end)
 
   it('history', function()