Enable --show-suppressed in JSON format

[knqyf263]

Description

--show-suppressed is currently available with the table format as documented. This is because this feature is still an experimental feature, and we don't want to encourage users to use the field in JSON. It makes it difficult to change the field schema in the future.

However, we found that some users still want to use it, so we output it in the JSON report with an explicit statement that it is subject to change in the future. Specifically, the field name “ExperimentalModifiedFindings” is used to clarify that this is experimental.

Discussed in #6479