Put the unbundled Linux executable in a subdirectory (#64992)

People frequently assume they can run the executable they find at the
top level of the build directory, and don't understand why they get
resource errors from the engine. To avoid that, this puts the unbundled
copy of the executable in a subdirectory with a name that should warn
people away from running it.

Fixes #64963

packages/flutter_tools/templates/app/linux.tmpl/CMakeLists.txt.tmpl

@@ -45,6 +45,14 @@ apply_standard_settings(${BINARY_NAME})
 target_link_libraries(${BINARY_NAME} PRIVATE flutter)
 target_link_libraries(${BINARY_NAME} PRIVATE PkgConfig::GTK)
 add_dependencies(${BINARY_NAME} flutter_assemble)
+# Only the install-generated bundle's copy of the executable will launch
+# correctly, since the resources must in the right relative locations. To avoid
+# people trying to run the unbundled copy, put it in a subdirectory instead of
+# the default top-level location.
+set_target_properties(${BINARY_NAME}
+  PROPERTIES
+  RUNTIME_OUTPUT_DIRECTORY "${CMAKE_BINARY_DIR}/intermediates_do_not_run"
+)
 
 # Generated plugin build rules, which manage building the plugins and adding
 # them to the application.