fix(combo): Handle selection when placed in an IgxGrid cell template and grid is virtualized - master

[ddaribo]

Closes #14305

Additional information (check all that apply):

• Bug fix
• New functionality
• Documentation
• Demos
• CI/CD

Checklist:

• All relevant tags have been applied to this PR
• This PR includes unit tests covering all the new code (test guidelines)
• This PR includes API docs for newly added methods/properties (api docs guidelines)
• This PR includes feature/README.MD updates for the feature docs
• This PR includes general feature table updates in the root README.MD
• This PR includes CHANGELOG.MD updates for newly added functionality
• This PR contains breaking changes
• This PR includes ng update migrations for the breaking changes (migrations guidelines)
• This PR includes behavioral changes and the feature specification has been updated with them

[RivaIvanova]

There are two strange behaviors:

1. Usually when opening the combo without a selected item, the first item is focused, however, when opening the combo on the 11th row (which let's say corresponds to the combo in the 1st row), the item that was selected in the 1st combo is focused in the 11th combo.
2. Once I select a value, I cannot deselect it. If I click the clear button, scroll down/up, and return to the combo the previous value is selected.

[ddaribo]

@RivaIvanova,

After further investigation, I believe these behaviors have to be addressed on the sample level. I’ve already logged an issue in igniteui-angular-samples (it is linked in the current PR’s issue also). More details are listed in its description. There is a pending PR for that as well.

To sum up, IMO the sample has to be adapted to support a virtualized scenario and the introduced changes will address the behaviors you have observed. Please, do test this branch along with the refactored sample (and by adding more records). This leaves this PR’s main task to resolve the error that was raised when scrolling a grid with templated combos with changing IDs, whose selection sets were not properly initialized in that case. I have also added commits that ensure closing the combo and losing its input focus when the ID is changing, for example while scorlling the grid.