bert_collector: Revise report format

Update the bert_collector to align with the latest schema format.
Entries are delimited by ===<filename>===.

Added and improved tests related to report format.

Bug: 375241111
Test: Bert report collected in expected format
Change-Id: I35fefa8e34afc9e6b9bea86b475c8e9016524bf9
4 files changed