[3.12] gh-131045: [Enum] fix flag containment checks when using values (GH-131053...

[3.12] gh-131045: [Enum] fix flag containment checks when using values (GH-131053) (#131232)

* gh-131045: [Enum] fix flag containment checks when using values (GH-131053)

Check would fail if value would create a pseudo-member, but that member
had not yet been created.  We now attempt to create a pseudo-member for
a passed-in value first.

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Co-authored-by: Ethan Furman <ethan@stoneleaf.us>
Co-authored-by: Tomas R. <tomas.roun8@gmail.com>