Adjust page-main container height for sticky footer; fixes #15118

[denistrator]

Description

Adjusted page-main container height for sticky footer. Added fix for Blank and Luma themes

Fixed Issues

#15118 Footers do not snap to bottom of screen on mobile devices

[magento-engcom-team]

Hi @denistrator. Thank you for your contribution
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[ihor-sviziev]

Related pull requests:
#15353
#16981

[magento-engcom-team]

Hi @denistrator. Thank you for your contribution.
We will aim to release these changes as part of 2.2.6.
Please check the release notes for final confirmation.

Please, consider to port this solution to 2.3 release line.
You may use Porting tool to port commits automatically.