Decompose Blockly.createDom_ in inject.js

[rachel-fenichel]

There are large chunks of code for the creation of filters, patterns, etc. In both scratch-blocks and Blockly those chunks should be broken out into helper functions.

In this file:

• lines 126-168 should become Blockly.createBlockFilters_(defs)
• lines 170-185 should become options.disabledPatternId = Blockly.createDisabledPattern_(defs, rnd)
• lines 187-207 should become options.gridPattern = Blockly.createGridPattern_(defs, rnd)

[rachel-fenichel]

Parallel issue in Blockly: google/blockly#1100