Add support for formatting-related requirements of PSR-12

[lkrms]

PrettyPHP's default formatting is largely PSR-12 compliant, but there are some differences to address.

Parts of PSR-12, e.g. PascalCase class names, fall outside the scope of a formatter and won't be implemented, although exceptions are sometimes made (use import statements are already sorted by default, for example).

• LF line endings
• Indent of 4 spaces
• Line length "SHOULD NOT" exceed 80 characters and "MUST" have a soft limit of 120 characters
• One statement per line (PreserveOneLineStatements must not be enabled)
• Blank lines after "header blocks" (SpaceDeclarations and SortImports mandatory):
  • <?php
  • file-level docblock (blank line only applied before namespace currently)
  • declare statements
  • namespace declaration
  • class use statements
  • function use statements
  • constant use statements
• Allow breaking over multiple lines if every item is on its own line (NoMixedLists mandatory):
  • implements and extends interfaces
    • Trigger if a newline appears after implements or extends, not just between first two interfaces
    • Add a newline before the opening brace of an anonymous class with an interface list that wraps
  • Parameters in function declarations
  • Variables in anonymous function use declarations
  • Arguments in function calls
  • Statements in for loops
• One-line declare at line 1 of files also containing markup: <?php declare(strict_types=1) ?>
  • Suppress newline before close tag even if present in source
• Force newlines before and after control structure expressions split over multiple lines
• Add whitespace between exception types in catch
• Enforce newline before first method in multiline method chains

[lkrms]

With the exception of line length enforcement, which is being tracked in #1, pretty-php's PSR-12 compliance is complete.