By Kate Holton and Paul Sandle LONDON (Reuters) -Britain vowed to repair the economic and social fabric of its “broken heartlands” on Wednesday, as the government set out a long-awaited plan to flesh out promises that helped Prime Minister Boris Johnson win a big parliamentary majority in 2019. With Johnson now reeling from public anger over lockdown parties held at his Downing Street residence, his government published plans to funnel investment into towns and regions to mitigate deep-rooted social and economic inequalities. Economists say geographical disparities in health, education and inc…