abg-writer: Refactor write_corpus API

abg-writer: Refactor write_corpus API

Introduce a new overload for write_corpus that follows the parameter
order context, object (i.e. corpus), indent.

Deprecate all other overloads that were part of the API and mostly
forward them to the new overload. That effort is made to ensure
write_context is always provided. write_context allows access to all
options that influence the output format.

	* include/abg-writer.h (write_corpus): Introduce new overload
	write_corpus(ctxt, corpus, indent) and deprecate all others.
	* src/abg-writer.cc (write_corpus): Likewise for the definitions
	and adjust.
	* tests/test-read-dwarf.cc (test_task::perform): Use the new
	write_corpus which requires a write_context.
	* tools/abidw.cc (load_corpus_and_write_abixml, ): Likewise.
	* tools/abilint.cc (main): Likewise. Also simplify logic around the
	locations as they now can be expressed with less code.

Signed-off-by: Matthias Maennich <maennich@google.com>