Upgrade align-self and align-items parsing to CSS 3

This change migrates the 2 properties to the CSS 3 Alignment
parsing. The new parsing is identical to how we parse
'justify-self'. The 2 properties need to be migrated together
as they are used in tandem in CSSComputedStyleDeclaration.

This change also removes EAlignItems as it is now unused.

BUG=249451

Review URL: https://codereview.chromium.org/134013002

git-svn-id: svn://svn.chromium.org/blink/trunk@165264 bbb929c8-8fbe-4397-9dbb-9b2b20218538