Heap - update property flattening on browserArrayLimit in track call

[jessi-heap]

Updated flattening logic

• when browserArrayLimit is set, it should still flatten objects outside of arrays
• added test should flatten properties on parent when browserArrayLimit is set shows an example of this case (objects are dropped in heap so we flatten here to retain the information)
• updated stringify logic - this was inconsistent
• removed the logic to remove the top level name from the key (should be custom_vars.xxx instead of xxx)

Testing

Include any additional information about the testing you have completed to
ensure your changes behave as expected. For a speedy review, please check
any of the tasks you completed below during your testing.

• Added unit tests for new functionality
• Tested end-to-end using the local server
• [Segmenters] Tested in the staging environment

[tcgilbert]

hi @jessi-heap - our partner engineer who reviews these PRs is currently out of office but will be back Thursday. If there is absolute urgency behind this PR, or you have any questions, let me know.

[joe-ayoub-segment]

hi @jessi-heap this PR has been deployed. Can you confirm that you are happy with the changes please?