SUJATA RAO AN unrelenting squeeze on the supply of global shares and sovereign bonds shows little sign of easing next year, with companies and central banks predicted to be big buyers of these securities in direct competition with investors. The supply mismatch could help to sustain the decade-long bull run in global equities and also keep bond yields at very low levels. A string of high-profile intial public offerings, as well as emergency secondary listings, this year raised almost $1 trillion in new equity, Dealogic data shows. Yet this flood of new equity issues did not end the supply squeeze…