Inline html tags followed by a newline break rich text rendering

[b-kelly]

Describe the bug

Reported on MSE.

When inline html tags appear on their own line, rich text mode parses the result incorrectly.

https://meta.stackexchange.com/q/379037/395497

To Reproduce

1. In markdown mode, add the following content:

Any text here, doesn't matter what.

<sub>
Any text is fine here, but note the html on their own lines
</sub>

2. Switch over to rich text mode
3. Note that the editor is completely empty

Expected behavior

At the very least, the opening paragraph and the text between the tags should be appearing. The tags should either be:

1. shown as plain text
2. used as intended to add a sub mark to the text inside

Additional context

This looks like an issue in the way we're parsing inline html tokens. The markdown-it parser demo parses the tokens as:

p_open + (inline > text) + p_close +
html_block

while we're parsing them as:

p_open + (inline > text) + p_close +
p_open + (inline > sub_open) + p_close +
p_open + (inline > text) + p_close +
p_open + (inline > sub_close) + p_close +

[b-kelly]

Updated code to only parse inline html tags if the opening and closing tags are on the same line