Add bfd_get_file_size to get archive element size

Add bfd_get_file_size to get archive element size

We can't use stat() to get archive element size.  Add bfd_get_file_size
to get size for both normal files and archive elements.

bfd/

	PR binutils/21519
	* bfdio.c (bfd_get_file_size): New function.
	* bfd-in2.h: Regenerated.

binutils/

	PR binutils/21519
	* objdump.c (dump_relocs_in_section): Replace get_file_size
	with bfd_get_file_size to get archive element size.
	* testsuite/binutils-all/objdump.exp (test_objdump_f): New
	proc.
	(test_objdump_h): Likewise.
	(test_objdump_t): Likewise.
	(test_objdump_r): Likewise.
	(test_objdump_s): Likewise.
	Add objdump tests on archive.