Split view conversion headers into components/view/conversions/ subdirectory (facebook#55709)

Summary:
Pull Request resolved: facebook#55709

The monolithic `conversions.h` (1785 lines) and several other conversion-related
headers made the view directory hard to navigate. This splits them into
domain-specific files under a new `conversions/` subdirectory:

- `YogaLayout.h` — Yoga float conversions, layoutMetricsFromYogaNode
- `YogaStyle.h` — fromRawValue for yoga enums, convertRawProp(yoga::Style)
- `Transform.h` — transform/transformOrigin parsing
- `ViewStyle.h` — fromRawValue for view style enums, CascadedRectangle helpers
- `Events.h` — convertRawProp(ViewEvents)
- `Background.h/cpp` — background image/gradient conversions
- `DebugString.h` — debug string toString overloads
- `CSSPrimitives.h` — CSS color/length/angle coercion helpers
- `Filter.h` — filter parsing
- `BoxShadow.h` — box shadow parsing
- `Accessibility.h` — accessibility trait/role/state conversions

Forwarding headers are left at old paths (`conversions.h`,
`accessibilityPropsConversions.h`, `propsConversions.h`) so external consumers
continue to compile unchanged. Internal consumers (`BaseViewProps.cpp`,
`ConversionsTest.cpp`) are updated to use the new paths directly.

All file copies use `sl copy` to preserve blame history.

Changelog: [Internal]

Differential Revision: D94169104

Author: NickGerleman

packages/react-native/ReactCommon/react/renderer/components/view/BackgroundImagePropsConversions.h

@@ -10,10 +10,9 @@
 #include <algorithm>
 
 #include <react/featureflags/ReactNativeFeatureFlags.h>
-#include <react/renderer/components/view/BackgroundImagePropsConversions.h>
-#include <react/renderer/components/view/BoxShadowPropsConversions.h>
-#include <react/renderer/components/view/FilterPropsConversions.h>
 #include <react/renderer/components/view/conversions.h>
+#include <react/renderer/components/view/conversions/BoxShadow.h>
+#include <react/renderer/components/view/conversions/Filter.h>
 #include <react/renderer/components/view/primitives.h>
 #include <react/renderer/components/view/propsConversions.h>
 #include <react/renderer/core/graphicsConversions.h>

packages/react-native/ReactCommon/react/renderer/components/view/BaseViewProps.cpp

@@ -15,6 +15,7 @@ react_native_android_selector(platform_SRC
 )
 file(GLOB rrc_view_SRC CONFIGURE_DEPENDS
         *.cpp
+        conversions/*.cpp
         ${platform_SRC})
 
 add_library(rrc_view OBJECT ${rrc_view_SRC})