DataGrid: enhance row update handling for editing item

[paulosdfigueiredo]

Update the logic for invoking the RowUpdated event to differentiate between internal and external editing modes.

Description

Closes #6178

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 not to work as expected)

Checklist:

• The PR is submitted to the correct branch (master for dev, rel-1.x for maintenance).
• My code follows the code style of this project.
• I've added relevant tests.

[stsrki]

Tested and it seems to be working.

Thanks for the work.