Use atPhase instead of inContext where possible

Author: odersky

compiler/src/dotty/tools/backend/jvm/BTypesFromSymbols.scala

@@ -229,7 +229,7 @@ class BTypesFromSymbols[I <: DottyBackendInterface](val int: I) extends BTypes {
       // After lambdalift (which is where we are), the rawowoner field contains the enclosing class.
       val enclosingClassSym = {
         if (innerClassSym.isClass) {
-          inContext(ctx.withPhase(ctx.flattenPhase.prev)) {
+          atPhase(ctx.flattenPhase.prev) {
             toDenot(innerClassSym).owner.enclosingClass
           }
         }

compiler/src/dotty/tools/backend/jvm/DottyBackendInterface.scala

@@ -137,7 +137,7 @@ object DottyBackendInterface {
         // for example by specialization
         val original = toDenot(sym).initial
         val validity = original.validFor
-        inContext(ctx.withPhase(validity.phaseId)) {
+        atPhase(validity.phaseId) {
           toDenot(sym).isStatic
         }
       }
@@ -149,7 +149,7 @@ object DottyBackendInterface {
       // it is very tricky in presence of classes(and annonymous classes) defined inside supper calls.
       if (sym.exists) {
         val validity = toDenot(sym).initial.validFor
-        inContext(ctx.withPhase(validity.phaseId)) {
+        atPhase(validity.phaseId) {
           toDenot(sym).lexicallyEnclosingClass
         }
       } else NoSymbol

compiler/src/dotty/tools/dotc/core/SymDenotations.scala

@@ -2201,7 +2201,7 @@ object SymDenotations {
     def ensureFreshScopeAfter(phase: DenotTransformer)(using Context): Unit =
       if (ctx.phaseId != phase.next.id) ensureFreshScopeAfter(phase)(using ctx.withPhase(phase.next))
       else {
-        val prevClassInfo = inContext(ctx.withPhase(phase)) {
+        val prevClassInfo = atPhase(phase) {
           current.asInstanceOf[ClassDenotation].classInfo
         }
         val ClassInfo(pre, _, ps, decls, selfInfo) = classInfo