Configure/Customize ruamel.yaml Loading and Dumping

[cognifloyd]

This configures and improves ruamel.yaml based formatting. One goal is to be compatible with other YAML formatters like prettier. It requires extending several ruamel.yaml components in ansiblelint.yaml_utils:

ansiblelint.yaml_utils.	extends ruamel.yaml.	For Loading	For Dumping
FormattedYAML	YAML	✅	✅
CustomConstructor	constructor.RoundTripConstructor	✅
FormattedEmitter	emitter.Emitter		✅
OctalIntYAML11	scalarint.ScalarInt	✅	✅

Each of these components serves the following purposes:

• FormattedYAML:
  • For Loading and Dumping:
    • Default to YAML 1.1 instead of YAML 1.2 (PyYAML does not support 1.2 so Ansible does not support it either)
      • this fixes boolean and octal identification and dumping (and possibly other issues)
  • For Loading:
    • Wire up CustomConstructor
    • preserve more newlines when loading YAML files (ruamel.yaml was discarding blank lines if they only had spaces)
    • preserve preamble/header (comments before ---) which ruamel.yaml does not preserve
  • For Dumping:
    • Wire up FormattedEmitter
    • Adjusts/configures ruamel.yaml's defaults
      • enable explicit start (---) and disable explicit end (...)
      • Max dump width = 120
      • indent maps with 2 spaces; sequences with 4 (including dash)
    • Drop blank lines at end of file (it should have only one \n)
• CustomConstructor:
  • For Loading:
    • Identify YAML 1.1 style octals to preserve them with OctalIntYAML11. Without this, ruamel.yaml converted octals to ints in YAML 1.1.
• OctalIntYAML11:
  • For Loading:
    • When Octals get loaded, the CustomConstructor builds this special int subclass to preserve its format as an Octal
  • For Dumping:
    • Represents itself as a YAML 1.1 formatted octal 0123.
    • For YAML 1.2, ruamel.yaml loads octals as OctalInt, but that gets represented as a YAML 1.2 style octal 0o123.
• FormattedEmitter:
  • For Dumping:
    • Ensures that root-level sequences (playbooks, task files, etc) are not over-indented without sacrificing indents at other levels.
    • Changes ruamel.yaml scalar quoting preference from single- to double-quotes.
    • Drop extra spaces (eg at end of line)
    • Condense repeated blank lines so that there is only ever one blank line
    • Add white space in flow-style maps ({ key: value } instead of {key: value})

This builds on #1926, #1934, and #1936 (and others)
Extracted from #1828.

[cognifloyd]

OK. I think this is done and ready for review.

The changes to the formatting-after fixture files highlight the differences with prettier's formatting. And, since lint is passing, prettier is not trying to change the format created by FormattedYAML (in other words, FormattedYAML output is compatible with prettier's output).