[2.x cherry-pick] Prevent outbound buffer overwrite during chunking

Description

Problem: For large Assurance events, the way the outbound event is being read and converted to a string can cause un-necessary content being appended to the last chunk. This is because the content is read in to a buffer and converted to a string directly irrespective of the actual bytes read. So if the last chunk of data is smaller than the buffer size the remaining part from the buffer could be included.

Solution: As a solution, modify the reading algorithm to store the number of bytes actually read. Then when creating the string use only the portion of the bytes actually read.

Motivation and Context

feature/v-next was cut before the fix was made. This is a direct cherry-pick from 2.x. Problem: For large Assurance events, the way the outbound event is being read and converted to a string can cause un-necessary content being appended to the last chunk. This is because the content is read in to a buffer and converted to a string directly irrespective of the actual bytes read. So if the last chunk of data is smaller than the buffer size the remaining part from the buffer could be included.

Solution: As a solution, modify the reading algorithm to store the number of bytes actually read. Then when creating the string use only the portion of the bytes actually read.

How Has This Been Tested?

Unit tests
Manual tests

Screenshots (if appropriate):

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:

[ ] I have signed the Adobe Open Source CLA.
[ ] My code follows the code style of this project.
[ ] My change requires a change to the documentation.
[ ] I have updated the documentation accordingly.
[ ] I have read the CONTRIBUTING document.
[ ] I have added tests to cover my changes.
[ ] All new and existing tests passed.

adobe / aepsdk-assurance-android