Search for $${{B} _{c} ^+} \!\rightarrow {{\pi } ^+} {\mu ^+\mu ^-} $$ Decays and Measurement of the Branching Fraction Ratio $${\mathcal {B}} ({{B} _{c} ^+} \!\rightarrow {\psi {(2S)}} {{\pi } ^+} )/{\mathcal {B}} ({{B} _{c} ^+} \!\rightarrow {{J \Hspace{-1.66656Pt}/\hspace{-1.111pt}\psi }} {{\pi } ^+} )$$