Add line-breaks formatter and test cases.

[phensley]

Proposal from Joe Wanko:

JSON-T Formatter Spec: line-breaks
Arguments: None - operates on the input string directly
Behavior: Converts newline characters ("\n") to HTML line break tags (<br/>).

Rationale: This formatter addresses the HTML whitespace collapsing issue where newlines in text content get compressed into single spaces. Converting \n to
ensures line breaks render correctly in HTML.

Edge Cases: Multiple consecutive newlines: Each "\n" becomes a <br/> (e.g., "\n\n" → <br/><br/>)
Empty string: Returns empty string
No newlines: Returns string unchanged

Input: "Line 1\nLine 2\nLine 3"
Output: "Line 1<br/>Line 2<br/>Line 3"

Usage Example

{quote | line-breaks}

[phensley]

@joewanko This change is released in version 2.11.0.