fix(grid): ensure resize observer is only created if available in ssr

[mddragnev]

Closes #17497

Description

Adding a guard that enables creating a resize observer only in browser mode.

Motivation / Context

Type of Change (check all that apply):

• Bug fix
• New functionality
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Refactoring (no functional changes)
• Documentation
• Demos
• CI/CD
• Tests
• Changelog
• Skills/Agents

Component(s) / Area(s) Affected:

How Has This Been Tested?

• Unit tests
• Manual testing
• Automated e2e tests

Test Configuration:

• Angular version:
• Browser(s):
• OS:

Screenshots / Recordings

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
• Accessibility (ARIA, keyboard navigation, focus management) has been verified

[Copilot]

Pull request overview

Adds an SSR-safe guard around ResizeObserver creation in the grid virtualization IgxGridForOfDirective to prevent server-side build/runtime errors when window/ResizeObserver are unavailable.

Changes:

• Avoid unconditional ResizeObserver instantiation by checking getResizeObserver() before creating viewObserver.
• Ensure SSR environments can initialize the directive without throwing due to missing browser APIs.

Suppressed comments (1)

projects/igniteui-angular/directives/src/directives/for-of/for_of.directive.ts:1683

• This SSR guard changes runtime behavior when ResizeObserver is missing (e.g., server build or non-DOM environment). Since this directive has an existing Jasmine spec suite, add a unit test that simulates window.ResizeObserver being unavailable and asserts that initialization does not throw.

        const resizeObserver = getResizeObserver();
        if (resizeObserver) {
            this.viewObserver = new resizeObserver((entries: ResizeObserverEntry[]) => this.viewResizeNotify.next(entries));
        }

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