Install Arrow C++ headers into wheel

Author: WillAyd

python/pyarrow/meson.build

@@ -390,19 +390,11 @@ py.install_sources(
     ),
     subdir: 'pyarrow/include/arrow/python',
 )
-#if arrow_dep.found()
-#    arrow_header_dir = arrow_dep.get_variable(
-# CMake has a local variable for ARROW_INCLUDE_DIR which is not
-# detectable from Meson
-# cmake: 'ARROW_INCLUDE_DIR',
-#        pkgconfig: 'includedir',
-#    ) / 'arrow'
-
-#    install_subdir(
-#        arrow_header_dir,
-#        install_dir: py.get_install_dir() / 'pyarrow/include',
-#    )
-#endif
+
+install_subdir(
+    get_option('includedir') / 'arrow',
+    install_dir: py.get_install_dir() / 'pyarrow/include',
+)
 
 py.install_sources(
     files('src/arrow/python/vendored/pythoncapi_compat.h'),