[RNMobile] Flatten inner blocks to fix call stack size exceeded crash - #54380

What?

This PR expands the block list logic to avoid having deeply nested inner blocks, which leads to crashing the editor. The idea is to identify the group blocks that don’t include any visuals when rendering the inner blocks, and dynamically remove them in the spirit of flattening the content structure.

Why?

Fixes wordpress-mobile/WordPress-Android#18750.
Fixes wordpress-mobile/gutenberg-mobile#6123.

How?

Extract the logic that calculates the block IDs to render in the block list component

This logic hasn't been modified, as it remains as it was before the PR:

Detect when inner blocks can be flattened

The inner blocks of a block can be flattened if the following conditions are met:

• The block has nested inner blocks.
• The block is an inner block of another block.
• The block is not selected. If the block is selected we need to render it to allow the user to edit it.
• The block type allows the flattening via the canFlattenInnerBlocks setting. This is a per-block setting, as the block is the one to determine if its inner blocks can be flattened.

Flatten inner blocks

This functionality basically iterates through all inner blocks, including the nested ones. If it determines that a block opts to flatten its inner blocks, they will be rendered by the parent.

Testing Instructions

[TBD]

Testing Instructions for Keyboard

N/A

Screenshots or screencast

N/A