Description:
add filter in Validity drop-down list while entering value to cell. 
If I have over 100 value in cells and I use them in Validity (cell range), then i must long scroll this long long drop-down list to find need item.
I offer add filter while entering value to cell with Validity, that make less list of variants 

Steps to Reproduce:
1. Create Validity , variant - cell range for any cell in spreadsheet
2. Use many cells with values for this cell range
3. Select your cell with Validity and open drop-down list
4. Find value needed to you. Good, if this value was in begin of list. And if not? You must scroll long list and carefully see to values to find needed value to you =(

Actual Results:  
we have long list of values in cell with Validity and there isn't filtering for it

Expected Results:
we can begin entering of value in the cell and we'll have short list of values in our list


Reproducible: Always


User Profile Reset: No



Additional Info:


User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:58.0) Gecko/20100101 Firefox/58.0