Refactor RCLMacros test into a shared example group

This way, we can test RCLFrame() and RCLAlignment() identically.
Clarify that layouts are based on intrinsic bounds
Test that layouts start with the intrinsic bounds
rcl_rect tests
rcl_size and rcl_origin tests
rcl_width and rcl_height tests
Simplify tests a bit (share more code)
rcl_center, rcl_centerX, and rcl_centerY tests
Remove old test (now basically obsoleted)
rcl_left and rcl_right tests
rcl_top and rcl_bottom tests
rcl_leading and rcl_trailing tests
rcl_baseline should always be based on alignment rects
Fix iOS target barfing on RCL imports in a RCL header
rcl_baseline tests