Whitespace immediately following the asterisk is not stripped in block comments

[sgrekhov]

According to the dartdoc specification.

Any whitespace immediately following the asterisk is also stripped, if present.

But it isn't so. In case

/**  Text.
 *     More text.
 */

The expected output is

Text.
More text.

Actual output:

Expected: 'Text.\n'
            'More text.'
  Actual: 'Text.\n'
            '    More text.'

See https://github.com/dart-lang/dartdoc/blob/main/test/co19/block_based_doc_comments_test.dart, the test test_removeWhitespaceAfterAsterisk().