Made JSON heuristic handle whitespace around structural characters correctly

[whiskeysierra]

Description

The JSON heuristic doesn't recognize {}\n as valid JSON.

Motivation and Context

JSON generators that produce formatted JSON will most likely append a trailing new line. The inlining of JSON bodies doesn't work for those.

Insignificant whitespace is allowed before or after any of the six
structural characters.

https://tools.ietf.org/html/rfc4627#section-2

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.

[lerovitch]

👍