Moved the new abstract functions of ExprOps to SubTreeOps.scala

src/main/scala/leon/frontends/scalac/CodeExtraction.scala

src/main/scala/leon/purescala/ExprOps.scala

src/main/scala/leon/purescala/SubTreeOps.scala

src/main/scala/leon/xlang/AntiAliasingPhase.scala

src/main/scala/leon/xlang/ImperativeCodeElimination.scala

src/main/scala/leon/xlang/XLangDesugaringPhase.scala

...t/resources/regression/frontends/error/xlang/Array2.scala

...t/resources/regression/frontends/error/xlang/Array3.scala

...t/resources/regression/frontends/error/xlang/Array5.scala

...t/resources/regression/frontends/error/xlang/Array7.scala

...ession/verification/xlang/valid/ArrayParamMutation1.scala

...ession/verification/xlang/valid/ArrayParamMutation2.scala

...ession/verification/xlang/valid/ArrayParamMutation3.scala

...ession/verification/xlang/valid/ArrayParamMutation4.scala

...ession/verification/xlang/valid/ArrayParamMutation5.scala

...ession/verification/xlang/valid/ArrayParamMutation6.scala

...ession/verification/xlang/valid/ArrayParamMutation7.scala

...ession/verification/xlang/valid/ArrayParamMutation8.scala

...ession/verification/xlang/valid/ArrayParamMutation9.scala

...n/verification/xlang/valid/NestedFunParamsMutation1.scala