[wip] Changes for extracting new router package

[jamiebuilds]

• Newer versions of Prettier have different defaults for arrowParens so I added arrowParens: avoid to your config so it wouldn't change the code style if someone is running a newer version of prettier
• Removed all of the block() related code
• Replaced usages of substr() (which is deprecated) with substring(), this didn't change how you were using it
• Removed all of the action related code. I can revert this if the scroll restoration work does end up needing it
• Removed all of the index tracking in a separate commit, it was only needed for block()
• Separate commit that updates tests for the action removal
• Refactored the common logic between browser and hash history into a createUrlBasedHistory() function

[jamiebuilds]

Size diff

history.production.min.js (gz) - Before: 2.06 kB - After: 1.19 kB

(edit: had wrong before size previously)