Support thematic breaks

[mportiz08]

Bug/issue #, if applicable: 125507297

Summary

Adds support for rendering "thematic breaks" within content using the <hr> element.

With the corresponding Swift-DocC PR, the markdown syntax for horizontal rules can be used in content to indicate a thematic break within content, and this PR adds rendering support for this.

Example Markdown:

diff --git a/SwiftDocCRender.docc/contributing/Internals.md b/SwiftDocCRender.docc/contributing/Internals.md
index d3054747..2500a12d 100644
--- a/SwiftDocCRender.docc/contributing/Internals.md
+++ b/SwiftDocCRender.docc/contributing/Internals.md
@@ -6,6 +6,8 @@ Learn how DocC-Render is built internally, the principles behind its structure,
 
 DocC-Render supports rendering reference pages, tutorials, and articles to document your project in a structured manner.
 
+---
+
 Each page fetches its required render JSON asynchronously, from the `/data` directory. To learn more about the types of pages DocC-Render supports, visit the [DocC Docs](https://www.swift.org/documentation/docc).
 
 ### Modular Architecture

Example rendering:

Dependencies

swiftlang/swift-docc#865

Testing

Steps:

1. Checkout/build the branch of Swift-DocC from Support thematic breaks #865
2. Checkout/build the branch of Swift-DocC-Render from this PR
3. Add/modify content with a markdown horizontal rule (like the example above)
4. Preview the docs using DOCC_HTML_DIR=/path/to/swift-docc-render/dist swift run docc preview ExampleContent.docc and verify that a horizontal rule is rendered in the appropriate place

Checklist

Make sure you check off the following items. If they cannot be completed, provide a reason.

• Added tests
• Ran npm test, and it succeeded
• Updated documentation if necessary

[mportiz08]

@swift-ci test

[emilyychenn]

This works great when I test it locally with my version of swift-docc (from here)! Just curious, is the thematic break supposed to have more emphasis than the horizontal line between the "Overview" and "Topics" sections?

[marinaaisa]

I tested it and it works great!
I added a comment to fix how hr looks by default.

Btw, you missed the docc executable in the testing instructions, if you want to update them:

DOCC_HTML_DIR=/path/to/swift-docc-render/dist swift run docc preview ExampleContent.docc

[mportiz08]

This works great when I test it locally with my version of swift-docc (from here)! Just curious, is the thematic break supposed to have more emphasis than the horizontal line between the "Overview" and "Topics" sections?

No, it should probably look the same. Thanks for catching that!

[mportiz08]

@swift-ci test

[mportiz08]

This works great when I test it locally with my version of swift-docc (from here)! Just curious, is the thematic break supposed to have more emphasis than the horizontal line between the "Overview" and "Topics" sections?

No, it should probably look the same. Thanks for catching that!

Fixed

[marinaaisa]

LGTM!

[mportiz08]

@swift-ci test