Support copy-paste from external spreadsheets

Background:
I was trying to copy a portion of an existing spreadsheet which is in Libreoffice calc (in .ods format) to Frappe Sheets but i couldn't. The import feature works fine but in cases where i only want to copy-paste a portion of the sheet, it does not support.

Steps to reproduce:
i. Open any existing spreadsheet which is not Frappe Sheets
ii. Copy the data from their and try to paste it in Frappe Sheets

Expected Behaviour:
The Data from the existing spreadsheet (non Frappe Sheets) should appear in Frappe Sheets

Reproduce the issue by copying a selected range from LibreOffice Calc into Frappe Sheets, then trace the existing paste handling and compare it with the import behavior. Done means data copied from an external spreadsheet appears correctly in Frappe Sheets without requiring a full import.

Written by the indexing model from the issue text.