Switch the C++ new expression over to InitializationSequence, rather

Switch the C++ new expression over to InitializationSequence, rather
than using its own partial implementation of initialization.

Switched CheckInitializerTypes over to
InitializedEntity/InitializationKind, to help move us closer to
InitializationSequence.

Added InitializedEntity::getName() to retrieve the name of the entity,
for diagnostics that care about such things.

Implemented support for default initialization in
InitializationSequence.

Clean up the determination of the "source expressions" for an
initialization sequence in InitializationSequence::Perform.

Taught CXXConstructExpr to store more location information.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@91492 91177308-0d34-0410-b5e6-96231b3b80d8