Ignore backticks in documentation abstracts

[natecook1000]

The linguistic tagger doesn't do a great job recognizing backticks as opening vs. closing quotes, so some valid abstracts that contain backticks were being rejected by the BeginDocumentationCommentWithOneLineSummary rule. This change removes any InlineCode nodes from the abstract paragraph before processing, since they aren't important to that judgment.

Fixes #924.

[ahoppen]

Does this cause issues when you have a code block that contains a period and would thus recognize it as a multi-sentence first paragraph?

Eg.

/// The same as `Foo.foo()`.
func bar() {}

If not, could you add a test case for that?

[allevato]

We can assume that a sentence-ending period will never occur inside an inline code block, so I wonder if we should simply remove the content within backticks before doing this check, instead of removing just the backticks.

Since the briefSummary field is already a Paragraph node, we could do this in a structured way by just locally mutating that tree to remove any InlineCode children (and likewise for SymbolLink children, to handle the DocC-style double-backtick syntax).

The only thing I'm not sure about is how the linguistic tagger would handle a space before the period, because I'm assuming that removing the InlineCode node from this:

Foo bar `baz`.

would leave us with "Foo bar .", and I'm not familiar enough with that API to know if it would handle that. If that's a problem, then we could address that by instead of removing the InlineCode/SymbolLink children, replacing them with a plaintext word like "placeholder", and then run the linguistic tagger on that result.

[natecook1000]

I would have sworn I updated this commit before opening the PR, but here we are. @allevato, I switched to use a MarkupRewriter to remove InlineCode nodes, and it seems to work great! I added a test case using a double-backtick link (which I don't think should have periods, but just in case) and it seemed to do fine.

[allevato]

This turned out super elegant. Thanks for the fix!