fix(core): rely on resize observer instead of window resize event

[N1XUS]

Related Issue.

Closes #6848

Description

Changed resize trigger. Now using ResizeObserver class instead of window resize event.
To check that resize spy works correctly, visit this example and check second column content: https://fundamental-ngx-gh--pr6940-fix-6848-resize-obse-dt0983a2.web.app/fundamental-ngx#/core/dynamic-page#layout

Please check whether the PR fulfills the following requirements

During Implementation

1. Visual Testing:

• visual misalignments/updates
• check Light/Dark/HCB/HCW themes
• RTL/LTR - proper rendering and labeling
• responsiveness(resize)
• Content Density (Cozy/Compact/(Condensed))
• States - hover/disabled/focused/active/on click/selected/selected hover/press state
• Interaction/Animation - open/close, expand/collapse, add/remove, check/uncheck
• Mouse vs. Keyboard support
• Text Truncation

2. API and functional correctness

• check for console logs (warnings, errors) -> There's an error message in console which is reproducible in main branch
• API boundary values
• different combinations of components - free style
• change the API values during testing

3. Documentation and Example validations

• missing API documentation or it is not understandable
• poor examples
• Stackblitz works for all examples

4. Accessibility testing
5. Browser Testing - Edge, Safari, Chrome, Firefox

PR Quality

• the commit message(s) follows the guideline:
  https://github.com/SAP/fundamental-ngx/blob/main/CONTRIBUTING.md
• tests for the changes that have been done
• all items on the PR Review Checklist are addressed :
  https://github.com/SAP/fundamental-ngx/wiki/PR-Review-Checklist
• Run npm run build-pack-library and test in external application
• update README.md
• Breaking Changes Wiki

PR Review

• visual misalignments/updates
• check Light/Dark/HCB/HCW themes
• RTL/LTR - proper rendering and labeling
• responsiveness(resize)
• Content Density (Cozy/Compact/(Condensed))
• States - hover/disabled/focused/active/on click/selected/selected hover/press state
• Interaction/Animation - open/close, expand/collapse, add/remove, check/uncheck
• Mouse vs. Keyboard support
• Text Truncation

2. API and functional correctness

• check for console logs (warnings, errors)
• API boundary values
• different combinations of components - free style
• change the API values during testing

3. Documentation and Example validations

• missing API documentation or it is not understandable
• poor examples
• Stackblitz works for all examples

4. Accessibility testing
5. Browser Testing - Edge, Safari, Chrome, Firefox

[netlify]

✔️ Deploy Preview for fundamental-ngx ready!

🔨 Explore the source changes: f7e997d

🔍 Inspect the deploy log: https://app.netlify.com/sites/fundamental-ngx/deploys/61712d23b6aa780008023c4d

😎 Browse the preview: https://deploy-preview-6940--fundamental-ngx.netlify.app

[github-actions]

Visit the preview URL for this PR (updated for commit f7e997d):

https://fundamental-ngx-gh--pr6940-fix-6848-resize-obse-dt0983a2.web.app

_{(expires Sun, 24 Oct 2021 09:11:52 GMT)}

_{🔥 via Firebase Hosting GitHub Action 🌎}