Refactor: Improves BottomBarButton padding logic.

[gstamatop]

Description of changes

• Refactor bottom bar buttons to receive a modifier for padding instead of PaddingValues.
• Update usages of bottom bar buttons in SuccessScreen, SelectCertificateScreen, and SelectQtspScreen to pass padding via modifier.
• Update ContentScreen to calculate paddings for sticky bottom content based on screen padding and layout direction.
• Update ScreenPadding.kt with a new function to calculate sticky bottom paddings.

Type of change

Please delete options that are not relevant.

• Other fix (maintenance or house-keeping)

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

• Test suite run successfully

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the readme
• My changes generate no new warnings
• I have added unit tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have checked that my views are accessible
• I have checked that my strings are localized where applicable