patch 9.1.0122: Some minor issues with the getregion() function

patch 9.1.0122: Some minor issues with the getregion() function

Problem:  Some minor issues with the getregion() function
Solution: Fix examples in the help, use OP_NOP op_type and MBLOCK
          as motion_type in f_getreg(), update vim syntax to
          for getregion() (Maxim Kim)

```
:xnoremap <CR>
\ <Cmd>echow getregion('v', '.', mode())<CR>
```
`echo` while in visual mode has no visible effect, thus people trying
example might be frustrated as it looks like nothing happens.

So the option is to change it to `echow` or `echom`.
With `echom` it is again has no visible effect but one can at least inspect `:messages`.
On the other hand `echow` showes selected text in a popup window.

```
Can also be used as a |method|: >
'.'->getregion("'a', 'v')
```

Here is the typo, which makes example invalid, should be `("'a", ...`

closes: #14064

Signed-off-by: Maxim Kim <habamax@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>