Support free-spacing mode Regexp in Naming/InclusiveLanguage

[sambostock]

WIP – See #11831.

This edits the way the Naming/InclusiveLanguage cop combines its config into Regexp to match terms. Specifically, because we would convert given Regexp to Strings via Regexp#source, and then simply combine patterns/strings using

Regexp.new(strings.join('|'), Regexp::IGNORECASE)

we would lose any mode/options information about the Regexp, which in the case of "free-spacing"/"extended" mode, would mean the Regexp could be corrupted by additional spacing being considered part of the pattern.

This changes the approach to normalize patterns as Regexps instead of Strings, and then simply combine them using Regexp.union. To preserve the existing behaviour of always making the patterns case insensitive, we extract the source and options from any given Regexp, and construct a new one where we force case insensitivity using

Regexp.new(regexp.source, regexp.options | Regexp::IGNORECASE)

This way, we preserve all other flags (/.../x, but also others like /.../m).

Note that it was previously possible to work around this by applying options at the subexpression level, which remains possible (e.g. to force case sensitivity).

TODO

• Validate approach
• Rename identifiers accordingly
• Add more specs for edge cases and covering existing behaviour, to ensure it is preserved.
• Better document use of Regexp in cop documentation (unclear how AllowedRegexp works; maybe separate PR?)

---

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• Wrote good commit messages.
• Commit message starts with [Fix #issue-number] (if the related issue exists).
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• Squashed related commits together.
• Added tests.
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[sambostock]

Could optimize to skip creating duplicates

Suggested change

	when Regexp then Regexp.new(object.source, object.options | Regexp::IGNORECASE)
	when Regexp
	return object if object.options == Regexp::IGNORECASE
	Regexp.new(object.source, object.options | Regexp::IGNORECASE)