runtime(dosbatch): Add syn-sync to syntax file

runtime(dosbatch): Add syn-sync to syntax file

Closing parentheses were often highlighted as errors.
Add a syntax sync command to reduce the error.

Also fix that `defined` was not highlighted as an operator inside
parentheses.  E.g.:
```
if defined foo (
    if defined bar (
        ...
    )
)
```
The first `defined` was highlighted but the second one was not.

related: #15453

Signed-off-by: Ken Takata <kentkt@csc.jp>
Signed-off-by: Christian Brabandt <cb@256bit.org>