Add a template attribute to the column block.

[andreilupu]

Description

After splitting the columns block into columns and column and along with the depreciation of grouped layouts in #7841 there is no way to declare a columns block with a default template.

So back then we could have a "Features block" with this default inner block:

<InnerBlocks
	templateLock={ false }
	layouts={ memoize( ( columns ) => {
		return Array.apply(null, Array(columns)).map((i, n) => ({
			name: `column-${ n + 1 }`,
			label: sprintf( __( 'Column %d' ), n + 1 ),
			icon: 'columns',
		} ) );
	} )(columns) }
	template={[
		['core/heading', {
			layout: 'column-1',
			content: 'Happiness'
		}],
		['core/heading', {
			layout: 'column-2',
			content: 'Flexibility'
		}],

		['core/paragraph', {
			layout: 'column-1',
			content: 'Lorem ipsum dolor sit amet elit do, consectetur adipiscing, sed eiusmod tempor incididunt ut labore et dolore magna aliqua.'
		}],
		['core/paragraph', {
			layout: 'column-2',
			content: 'Lorem ipsum dolor sit amet elit do, consectetur adipiscing, sed eiusmod tempor incididunt ut labore et dolore magna aliqua.'
		}]
	]}
/>

But now there is no way to do that because the column block doesn't take any props from parents.

This PR makes this possible by adding a template attribute to the column block which can be used like

<InnerBlocks
	templateLock={ 'all' }
	allowedBlocks={ [ 'core/column' ] }
	template={[
		[ 'core/column', {
			template: [
				['core/heading', {
					content: 'Happiness'
				}],
				['core/paragraph', {
					content: 'Lorem ipsum dolor sit amet elit do, consectetur adipiscing, sed eiusmod tempor incididunt ut labore et dolore magna aliqua.'
				}],
			]
		} ],
		[ 'core/column', {
			template: [
				['core/heading', {
					content: 'Flexibility'
				}],
				['core/paragraph', {
					content: 'Lorem ipsum dolor sit amet elit do, consectetur adipiscing, sed eiusmod tempor incididunt ut labore et dolore magna aliqua.'
				}],
			]
		} ],
	]}
/>

I know this is way too simple to be true, and I would love @aduth 's opinion on it.
Also, If this makes sense, I would love to try a "Features" block example on gutenberg-examples repository.

How has this been tested?

Screenshots

Types of changes

Non-breaking change which adds functionality)

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• My code has proper inline documentation.

[andreilupu]

This is not needed. I wasn't aware that you can pass child elements via templates.

@chrisvanpatten just provided me a better example

<InnerBlocks
	templateLock={ 'all' }
	allowedBlocks={ [ 'core/column' ] }
	template={[
		['core/column', {}, [
			['core/heading', {
				content: 'Happiness'
			}],
			['core/paragraph', {
				content: 'Lorem ipsum dolor sit amet elit do, consectetur adipiscing, sed eiusmod tempor incididunt ut labore et dolore magna aliqua.'
			}],
		]],
		['core/column', {}, [
			['core/heading', {
				content: 'Flexibility'
			}],
			['core/paragraph', {
				content: 'Lorem ipsum dolor sit amet elit do, consectetur adipiscing, sed eiusmod tempor incididunt ut labore et dolore magna aliqua.'
			}],
		]],
	]}
/>

Sorry for the noise

[chrisvanpatten]

Yay! Happy to help @andreilupu :)