fix(snippet): use <cmd>call cursor() for visual range

Problem:  Change applied in d3e495ce uses a byte-offset where a virtual
          column is expected.
Solution: Set the cursor directly through a <Cmd> mapping, while making
          sure the commands are ordered correctly by adding them to the
          type-ahead buffer.

test/functional/lua/snippet_spec.lua

@@ -307,4 +307,10 @@ describe('vim.snippet', function()
     ]]
     )
   end)
+
+  it('correct visual selection with multi-byte text', function()
+    test_expand_success({ 'function(${1:var})' }, { '口口function(var)' }, nil, '口口')
+    feed('foo')
+    eq({ '口口function(foo)' }, buf_lines(0))
+  end)
 end)