BANGKOK, Aug 22 (Reuters) – When Thailand's deposed prime minister Thaksin Shinawatra went into self-imposed exile in 2008 facing a raft of corruption charges following his ouster in a military coup, he issued a hand-written note. "If I am fortunate enough," wrote Thaksin, a deeply polarising telecoms billionaire who broke the mould of Thai politics, "I will return and die on Thai soil." On Tuesday, the 74-year-old flew into Bangkok on a private jet, just hours before the latest incarnation of the populist party he founded was due to make a bid for power in an alliance with parties linked…