fix(tab-bar): update to match MD design and remove transforms

[brandyscarney]

Short description of what this resolves:

Updates the tab-bar to match the MD bottom navigation spec: https://material.io/design/components/bottom-navigation.html#specs

Changes proposed in this pull request:

• moved flex properties to host, inherit in child anchor element
  • this allows the user to customize the tab-button flex properties & fixes Ionic 4: Tab button should justify content center #16231
• increased letter spacing
• removed transforms / transitions on active tab
• decreased badge size, add empty styles
• fix badge positioning on both iOS and MD
• updates e2e tests, adds a preview test for tab-bar
• updates documentation surrounding tabs

fixes #16231
fixes ionic-team/ionic-docs#175
fixes ionic-team/ionic-docs#163

Material Design

test	master	tab-bar-design
preview
scenarios

iOS

test	master	tab-bar-design
preview
scenarios

[brandyscarney]

This should be good to merge once checks pass. Ben approved.