change Node get methods to getters

[ianstormtaylor]

Right now when using State you can do:

state.blocks
state.text
state.marks
...

But with Nodes you have to do:

node.getBlocks()
node.getMarks()
node.isLeafBlock()
...

It would be nice to change this so that we stay consistent IMO.

A list of candidates:

  'getBlocks',
  'getBlocksAsArray',
  'getCharacters',
  'getCharactersAsArray',
  'getFirstText',
  'getInlines',
  'getInlinesAsArray',
  'getKeys',
  'getLastText',
  'getMarks',
  'getOrderedMarks',
  'getMarksAsArray',
  'getText',
  'getTextDirection',
  'getTexts',
  'getTextsAsArray',
  'isLeafBlock',
  'isLeafInline',

The complication is just figuring out how to handle the inheritance of getters, and then how to memoize them more performantly since they take no arguments.

[ianstormtaylor]

Given that we will be forced to do this with #2495 we can close this out.