Implement excel-style tree view in pivot grid.

[MayaKirova]

Closes #11049

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

[dkamburov]

Some of the values of the noop sample are not populated

Edit: For the noop sample those values should be (Blanks), remote operations implementing the strategy should handle populating the values for these cases.

[MayaKirova]

@dkamburov Should show empty item now in case noop strategies are used (same as in master).

[mddragnev]

@MayaKirova When applying initial filtering from pivot configuration to a dimension which have hierarchy, all other values in the ESF are not present.
For example: Setting this dimension in the pivot dev sample

 {
            memberFunction: () => 'All',
            memberName: 'AllProducts',
            enabled: true,
            width: '25%',
            childLevel: {
                memberFunction: (data) => data.ProductCategory,
                memberName: 'ProductCategory',
                enabled: true,
                filter: this.filterExpTree
            }
        },

And this filtering expression tree

this.filterExpTree.filteringOperands = [
            {
                condition: IgxStringFilteringOperand.instance().condition('equals'),
                fieldName: 'ProductCategory',
                searchVal: 'Clothing'
            }
        ];

[MayaKirova]

@mddragnev For the hierarchical filters, there's a slightly different format for the search values. They have to contain the full path to the child values that are included:
For example:

 this.filterExpTree.filteringOperands = [
            {
                condition: IgxStringFilteringOperand.instance().condition('equals'),
                fieldName: 'AllProducts',
                searchVal: "[All].[Clothing]"
            }, 
           {...}
        ];

And they need to be applied to the root:

{
            memberFunction: () => 'All',
            memberName: 'AllProducts',
            filter: this.filterExpTree,
            enabled: true,
            width: '25%',
            childLevel: {
                memberFunction: (data) => data.ProductCategory,
                memberName: 'ProductCategory',
                enabled: true
            }
        }