BHV-743: Compute index bounds for rows whenever metrics are changed.

Issue
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Making a DataGridList specific fix (as opposed to DataList) involving calculation of index bounds for the first and last rows, dependent on the column count.

Fix
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This has been moved to `updateMetrics` as the column count can change here and we want to keep these index bounds in sync with the columns.

Enyo-DCO-1.1-Signed-off-by: Aaron Tam <aaron.tam@lge.com>