Move from cmp --> eq, and provide a good implementation for interning

include/grpc/impl/codegen/slice.h

include/grpc/slice.h

src/core/ext/census/grpc_filter.c

src/core/ext/load_reporting/load_reporting_filter.c

src/core/ext/transport/chttp2/transport/chttp2_transport.c

src/core/ext/transport/chttp2/transport/hpack_encoder.c

src/core/ext/transport/chttp2/transport/hpack_parser.c

src/core/ext/transport/chttp2/transport/hpack_parser.h

src/core/ext/transport/chttp2/transport/hpack_table.c

src/core/ext/transport/chttp2/transport/parsing.c

src/core/lib/channel/compress_filter.c

src/core/lib/channel/http_client_filter.c

src/core/lib/channel/http_server_filter.c

src/core/lib/compression/compression.c

src/core/lib/iomgr/resource_quota.c

src/core/lib/security/transport/client_auth_filter.c

src/core/lib/security/transport/server_auth_filter.c

src/core/lib/slice/slice.c

src/core/lib/slice/slice_intern.c

src/core/lib/slice/slice_internal.h