Previously: https://github.com/WordPress/gutenberg/pull/3686/files#r185262287

Currently, a block implementer may need to anticipate that any of the following functions may be undefined if the post template is locked for editing:

• insertBlocksAfter
• onReplace
• mergeBlocks

Instead of placing the burden on the developer to differentiate between the type, we should simply pass it as a function regardless of whether the template is locked. If it is a locked template, the function should effectively be a noop.

Open questions:

• Are there valid use cases where a block implementer may legitimately want to distinguish characteristics of the block depending on whether the template is locked or not? This information is still available via withSelect, and could additionally be passed as a prop to the block's edit component.