Add support for one-line statement blocks with no braces

Problem/Motivation

Add support for one-line statement blocks with no braces. The current code adds braces to all block statements (conditionals, for, foreach, etc.). This change is needed to implement complete whitespace and comment preservation.

Proposed resolution

See patch(es).

Remaining tasks

Before committing, code will be reviewed, tested against D8 core files, and documentation updated.

User interface changes

Not applicable.

API changes

To be completed later.