December is mega-tax-bill time on Capitol Hill, when legislation loaded with gifts and goodies for special-interest constituents moves ahead for action before the end of the year. House Republicans have unveiled their 2018 version — nearly 300 pages worth — and it has goodies galore: Write-offs and tax-credit deals for racehorse owners, “motorsports entertainment complexes,” TV and film producers, mine-rescue team trainers, two-wheeled electric vehicles, Indian coal facilities, economic development in American Samoa and a bunch of others.