Added C-API specs for rb_class_real.
Fixed specs for rb_check_convert_type and rb_convert_type.
Added specs for rb_io_taint_check().

Added for #3057.
Added C-API spec for rb_exc_raise with empty backtrace.
Basic specs for INT2NUM / rb_int2num.
CAPI specs for rb_rational_num and rb_rational_den

This is based on MRI commit e56d2c38.
Specs for rb_big_cmp.
Added specs for rb_big_pack().
Added specs for rb_dbl2big().
Added specs for rb_intern_const().
Add specs for rb_funcall3
Added specs for CApi method rb_Array.
Added C-API specs for rb_std{in,out,err,defout}
Add specs for rb_funcall_with_block

This commit adds specs for `rb_funcall_with_block`.
Fix empty lines in rb_funcall_with_block spec
Add corner-case spec for ill-state string with no padding ByteArray
Fix minor typo

[skip ci]
Fix another minor typo

[skip ci]
Added C-API specs for rb_class_path.