Reduce changes to session history entry

[PaperStrike]

Motivation and Context

• Ignore session history entries that are not pushed / replaced by Pjax.
• Change window scroll restoration mode only when needed.
• Use the scrollRestoration option when leaving, not entering a page.

How Has This Been Tested?

Unfortunately, there isn't a test plan for src/index.ts, yet.

Screenshots (if appropriate):

Types of changes

• [ ] Bug fix (non-breaking change that fixes an issue)
• [ ] New feature (non-breaking change that adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)
• [x] Refactor (no bug fix and new feature but improvements)

Checklist:

• [ ] My change requires new tests.
• [ ] I have added tests to cover my changes.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.