analyzer: add SARIF property bags to taint diagnostics

Another followup to r14-6057-g12b67d1e13b3cf to make it easier to debug
the analyzer.

gcc/analyzer/ChangeLog:
	* sm-taint.cc: Include "diagnostic-format-sarif.h".
	(bounds_to_str): New.
	(taint_diagnostic::maybe_add_sarif_properties): New.
	(tainted_offset::tainted_offset): Add "offset" param.
	(tainted_offset::maybe_add_sarif_properties): New.
	(tainted_offset::m_offset): New.
	(region_model::check_region_for_taint): Pass offset to
	tainted_offset ctor.

Signed-off-by: David Malcolm <dmalcolm@redhat.com>