Fix autoload status of statically linked extensions

	Previously, for statically-linked extensions, we used
	`vm->loading_table` to delay calling the init function until the
	extensions are required. This caused the extensions to look like they
	are in the middle of being loaded even before they're required.
	(`rb_feature_p()` returned true with a loading path output.) Combined
	with autoload, queries like `defined?(CONST)` and `Module#autoload?`
	were confused by this and returned nil incorrectly. RubyGems uses
	`defined?` to detect if OpenSSL is available and failed when OpenSSL was
	available in builds using `--with-static-linked-ext`.

	Use a dedicated table for the init functions instead of adding them to
	the loading table. This lets us remove some logic from non-EXTSTATIC
	builds.

	[Bug #19115]
	---
	 load.c                     | 55 +++++++++++++++++++++++++++++++++++-----------
	 test/ruby/test_autoload.rb | 18 +++++++++++++++
	 vm.c                       |  3 +++
	 vm_core.h                  |  9 ++++++++
	 4 files changed, 72 insertions(+), 13 deletions(-)