Update templates to use recommended way of getting grid columns for Blazor

[skrustev]

Related to IgniteUI/igniteui-blazor-examples#816

[MarielaTihova]

- Issue 1
(also observed in prod, but the same console errors there appear as warnings):

When we want to show a chart, clicking on the chart button produces these console errors for sample /grids/grid/finjs

[MarielaTihova]

- Issue 2: 
(also observed in prod as console errors)

When exapnding rows, errors are shown in the console. The issue seems to be happening only the first time a row is being expanded. NOT observed when being collapsed. Also NOT observed when expanding the child elements of an already expanded row.

Sample: /grids/hierarchical-grid/data-summary-template

[MarielaTihova]

- Issue 2: 
(also observed in prod as console errors)

When exapnding rows, errors are shown in the console. The issue seems to be happening only the first time a row is being expanded. NOT observed when being collapsed. Also NOT observed when expanding the child elements of an already expanded row.

Sample: /grids/hierarchical-grid/data-summary-template

An issue for this bug has been created in Blazor examples repo. Marking this PR as 'verfied' and ready to be merged, as the issue is not being raised by it. It is only observed in the same Blazor examples.