Restore public parseUnprocessedTransformOriginString - #58893

Summary:

The Android react-native-unistyles job in the nightly tests has failed since the 20261003 nightly:

TransformOriginConverter.cpp:124:20: error: no member named
'parseUnprocessedTransformOriginString' in namespace 'facebook::react'

#58786 moved the transform-origin helpers from react/renderer/components/view/conversions.h into conversions.cpp. One of them, parseUnprocessedTransformOriginString, was an inline function in the public header, and it ended up in an anonymous namespace in the .cpp. Libraries can't call it anymore. Unistyles calls it on React Native 0.85 and newer (only when RN_SERIALIZABLE_STATE is defined, so in practice only on Android).

This change declares parseUnprocessedTransformOriginString(const std::string&, TransformOrigin&) in conversions.h again and moves its definition out of the anonymous namespace. The implementation stays in conversions.cpp, and the signature uses only std::string and TransformOrigin, so no CSS headers leak back into the public header. The other helpers #58786 made private stay private.

Changelog:

[GENERAL] [FIXED] - Restore public parseUnprocessedTransformOriginString in react/renderer/components/view/conversions.h

Test Plan:

• Regenerated the C++ API snapshots with Doxygen 1.16.1, the version CI uses: python -m scripts.cxx-api.parser. For the Common and Apple views, the only diff this change causes is one restored line: void facebook::react::parseUnprocessedTransformOriginString(const std::string& value, facebook::react::TransformOrigin& result);. That is the same line Make renderer View conversions CSS-free (#58786) #58786 removed. My local Apple output also had extra codegen entries for the sample TurboModule, so I left those out of the commit.
• In my environment the Android views fail to generate even on clean main (Identifier basic_appender already exists in scope v12). I added the same line by hand to the three Android snapshots, at the position Make renderer View conversions CSS-free (#58786) #58786 removed it from. The validate-cxx-api-snapshots job will confirm them.
• yarn format-check-cpp: no violations in repository files.
• I couldn't build the C++ locally, so I'm relying on CI for compilation. The change only moves an existing function definition out of an anonymous namespace and adds its declaration.
• After this lands, the Android unistyles job in the nightly tests should compile TransformOriginConverter.cpp again.