Boston Baroque has announced its 2019-20 season, which will include five concerts. The season will open with two Classical symphonies: Mozart’s “Linz” Symphony No. 36 in C major, and Haydn’s Symphony No. 102 in B flat. Soprano Amanda Forsythe will perform a set of virtuosic arias including “Barbaro, o Dio, mi vedi” from Mozart’s “Il re pastore,” “Ruhe sanft, mein holdes {…}