feat(h-grid): provide injector to simplify child toolbar template setup

[damyanpetev]

This allows the definition of child grid toolbar templates without the explicit need to get the grid ref and assign it to the toolbar.
So from:

<igx-row-island>
  <igx-grid-toolbar [grid]="childGrid" *igxGridToolbar="let childGrid">

to

<igx-row-island>
  <igx-grid-toolbar *igxGridToolbar>

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

[MayaKirova]

@damyanpetev LGTM.
I'm just wondering if maybe we should also deprecate/remove the grid property on to the toolbar as a whole. It seems to have been used only for child hierarchical grid, so if we no longer use it might be better to just remove it.
@dkamburov We'll need to update the docs for the next release for the hgrid toolbar for this change: https://www.infragistics.com/products/ignite-ui-angular/angular/components/hierarchicalgrid/toolbar

[damyanpetev]

@damyanpetev LGTM. I'm just wondering if maybe we should also deprecate/remove the grid property on to the toolbar as a whole. It seems to have been used only for child hierarchical grid, so if we no longer use it might be better to just remove it. @dkamburov We'll need to update the docs for the next release for the hgrid toolbar for this change: https://www.infragistics.com/products/ignite-ui-angular/angular/components/hierarchicalgrid/toolbar

I think the grid reference can still be useful for other use cases (perhaps custom buttons that call some grid API), so it could be left exposed. Wondering if we should expose it the same way for the paginator, but I digress.
And already on the docs change IgniteUI/igniteui-docfx#5713 :)

[MayaKirova]

@damyanpetev LGTM. I'm just wondering if maybe we should also deprecate/remove the grid property on to the toolbar as a whole. It seems to have been used only for child hierarchical grid, so if we no longer use it might be better to just remove it. @dkamburov We'll need to update the docs for the next release for the hgrid toolbar for this change: https://www.infragistics.com/products/ignite-ui-angular/angular/components/hierarchicalgrid/toolbar

I think the grid reference can still be useful for other use cases (perhaps custom buttons that call some grid API), so it could be left exposed. Wondering if we should expose it the same way for the paginator, but I digress. And already on the docs change IgniteUI/igniteui-docfx#5713 :)

The directive that holds the grid context can stay. I'm talking about this grid input that is no longer needed: https://github.com/IgniteUI/igniteui-angular/blob/master/projects/igniteui-angular/src/lib/grids/toolbar/grid-toolbar.component.ts#L58

I don't think the toolbar can be used outside of the grid. Since something like this:

    <igx-grid-toolbar [grid]="grid1">
        <igx-grid-toolbar-title>{{ toolbarTitle }}</igx-grid-toolbar-title>
    </igx-grid-toolbar>
    <igx-hierarchical-grid #grid1 ...

Thrown an injection error.

And judging by the api docs around the prop, it was used for the hierarchical grid children only, so maybe it can be removed now.
It can be logged separately of course, it just bugs me that it's there and seems to be useless now.