Bug - Block Quote Rendering Issues

Requested by: @tomek-i via YakShaver.ai cc: @tomek-i, @kulesy, @adamcogan, @JackDevAU

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Pain

A quote with two paragraphs comes back as one run of text with the words jammed together, and that collapse is written back to disk on save.

A list, a nested quote or a code block inside a quote fails harder: the parser throws, the entire rich-text field is replaced by a single invalid markdown block, and on the markdown parser path the save then fails outright.

Approach

One fix in the shared parse step covers both the mdx and the markdown parser, and v4 uses the same package.

Reported twice before and never fixed: https://github.com/tinacms/tinacms/issues/3118 and https://github.com/tinacms/tinacms/issues/3492. https://github.com/tinacms/tinacms/issues/4563 is the adjacent-quote merge, a different cause, and is out of scope here.

Acceptance Criteria

1. A quote with two paragraphs round-trips as two paragraphs, with no words jammed together.
2. A list inside a quote parses, renders and saves.
3. A nested quote and a fenced code block inside a quote do the same.
4. No block quote input leaves the field as an invalid markdown block, on either parser path.

Screenshot

Figure: Block quote rendering strips white spacing, resulting in a single block of text.