[Codegen 131]: add emitUnionProp in parser primitives

[Zwem]

Summary:

[Codegen 131] This PR add a function emitUnionProp to the parser-primitives, as requested on #34872

Changelog:

[INTERNAL] [ADDED] - Add emitUnionProp function to parser-primitives

Test Plan:

yarn test react-native-codegen

[Zwem]

@rshest Hi, sorry, but the previous PR was closed because of branch name changing(#38704)

[rshest]

@Zwem Sorry, I am a bit confused to what exactly had happened. Why was #38704 closed?

[facebook-github-bot]

@rshest has imported this pull request. If you are a Meta employee, you can view this diff on Phabricator.

[Zwem]

@rshest After creating PR I found this alert "The head ref may contain hidden characters: "\u0441odegen-131" because, in the named branch, I had the Cyrillic symbol 'с' instead of Latin 'c'. And after I renamed brunch in the proper way PR was closed.

[analysis-bot]

Platform	Engine	Arch	Size (bytes)	Diff
android	hermes	arm64-v8a	8,885,453	+2
android	hermes	armeabi-v7a	7,935,800	+0
android	hermes	x86	9,281,970	+1
android	hermes	x86_64	9,185,458	-1
android	jsc	arm64-v8a	9,473,451	-2
android	jsc	armeabi-v7a	8,416,807	-2
android	jsc	x86	9,456,195	-1
android	jsc	x86_64	9,772,408	-1

Base commit: 8bcfc49
Branch: main

[github-actions]

This pull request was successfully merged by @Zwem in 5eaf28b.

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