feat(simple-combo): allow values to be selected on tab press - master

[georgianastasov]

Closes #14085

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]

public data: any[] = [
    { id: 1, name: 'Apple' },
    { id: 2, name: 'Orange' },
    { id: 3, name: 'Mango' },
];

<igx-simple-combo
  [data]="data"
  [valueKey]="'id'"
  [displayKey]="'name'"
  [allowCustomValues]="true"
>
</igx-simple-combo>

Entering a value that does not exist in the data and pressing Tab throws an error.