[2.0.0-beta4] Component Validator: useless meta:enum

Problem/Motivation

Some meta:enum have identical keys and values:

'meta:enum':
  primary: primary
  secondary: secondary
  tertiary: tertiary
  black: black
  white: white

Sometimes, it is because of bad conversion #3475962: [2.0.0-beta4] Cleaner meta:enum conversion, sometimes it is because of component author negligence.

Proposed resolution

It is not a big deal, it works very well, but it is useless and it is a second list to keep synchronized.

So, let's print a warning when ALL the items of a meta:enum have similar data in keys and enums.

So, this is OK (because it looks deliberate):

'meta:enum':
  sm: Small
  md: md
  lg: lg