CS: normalize code style rules [1]

[jrfnl]

Description

• PHPCS config: sync an exclusion
  ... with the same exclusion in the .gitattributes file.
• CS: don't use double quotes where not needed
• CS: no unnecessary heredocs
• CS: forbid join alias function
• CS: enforce consistent formatting of return types

Suggested changelog entry

N/A

Related issues/external references

Part of a series of PRs to address #155