Refactor H5FD and package initialization

[qkoziol]

• Reverts PR#1024, which (unnecessarily) switched from deferred package initialization to centralized initialization of all packages and introduced H5FDperform_init() to wrap an internal routine to initialize VFD plugins.
• Went back to deferred package initialization (primarily), to eliminate unnecessary resource use. (Performance has been verified to be the same either way)
• Switched VFD plugins to use “#define (H5OPEN, )” pattern, with registration of internal VFD plugins at library initialization time. Eliminates calling API routine (H5FDperform_init) from within library, which was deadlocking threadsafe concurrency. And also eliminates exposing internal library routines in a public header file.
• Removed copy-and-paste replicas of the H5OPEN macro and put a (better) single definition in H5public.h
• Separated API and internal routine calls in stdio and multi VFD plugins into separate source files, so that the library doesn’t invoke API routines internally (also a deadlock problem for threadsafe concurrency). Also needed a “private” header for these plugins.
• Separated registering/unregistering a VFD plugin from initializing/finalizing the plugin, instead of blurring those ideas together. Defers the VFD plugin init to when it’s actually used, which reduces resource usage, especially for the MPI-based plugins like the subfiling, etc.
• Refactored the copy-and-pasted check for locking into a central location in the H5FD.c code.
• Fixed a bunch of compiler warnings, especially ones that trigger CI failures with -Werror