Inconsistency? PAIR_HTML_COMMENT token not available in BLOCK_HTML

I noticed that when one uses HTML comments inside a regular paragraph, the token tree contains `PAIR_HTML_COMMENT → HTML_COMMENT_START` and eventually `PAIR_HTML_COMMENT → HTML_COMMENT_STOP` (the → denotes is-a-child)

This makes applying highlight colors to HTML comments a bit weird since the comment range is sometimes available as `PAIR_HTML_COMMENT`, sometimes not. Maybe something odd is underlying all this that you might want to know about @fletcher

## Observations

When you put the HTML comment on its own line in an empty document or at the _end_ of a document _without a trailing newline_, it's the same, e.g.:

```
BLOCK_PARA
PAIR_HTML_COMMENT
HTML_COMMENT_START
TEXT_PLAIN ...
HTML_COMMENT_STOP [after this is EOF]
```

But when the HTML comment spans the whole line and ends in a newline character, the token tree is:

```
BLOCK_HTML
HTML_COMMENT_START
TEXT_PLAIN ...
HTML_COMMENT_STOP
TEXT_NL
BLOCK_EMPTY [here is EOF]
```

Note that this seems to be a special case, because the following in a Markdown document ...

```

```

... produces `BLOCK_HTML` with multiple `LINE_HTML` tokens, _except_ for the line with the HTML comment; the tokens from that line stand alone. Here's some debug output with token types and the ranges (location + length):

```
{0,35}TokenType.blockHtml
{0,6}TokenType.lineHtml

{28,1}TokenType.angleLeft
{29,1}TokenType.slash
{30,3}TokenType.textPlain
{33,1}TokenType.angleRight
{34,1}TokenType.textNl
{35,0}TokenType.blockEmpty
```

### Exceptions from the rule?

Oddly enough, when you have a multi-line HTML comment:

```

```

This is not at all recognized as `BLOCK_HTML`, but `BLOCK_PARA` instead, and it includes a `PAIR_HTML_COMMENT`.

Plus if you add empty newlines around "foo" here, the whole `HTML_COMMENT_PAIR` is dissolved again and you have multiple paragraph blocks, one including the start, one the stop token.