fix(heading): initially follow theme's margin if OceanWP is used

[Arukuen]

fixes #3259

[github-actions]

🤖 Pull request artifacts

file	commit
pr3349-stackable-3349-merge.zip	b20abc4

[github-actions]

Try this Pull Request in the WordPress playground: https://playground.wordpress.net/?mode=seamless#{"landingPage":"/wp-admin/post-new.php?post_type=page","preferredVersions":{"php":"latest","wp":"latest"},"steps":[{"step":"login","username":"admin","password":"password"},{"step":"installPlugin","pluginZipFile":{"resource":"url","url":"https://raw.githubusercontent.com/gambitph/Stackable/artifacts/pr3349-stackable-3349-merge.zip"}}]}

[bfintal]

Since the issue is with OceanWP only, it would be better to have a fix that would be applicable only with OceanWP and only targets the issue. Adjusting all blocks for all scenarios would pose more issues. Also, we have default margins for our blocks, this removes them