This Cl updates the names of the initializer expressions to be clearer.
* InitializerExpression -> ConstructorExpression
* ConstInitializerExpression -> ScalarConstructorExpression
* TypeInitializerExpression -> TypeConstructorExpression
Bug: tint:26
Change-Id: Ib046497f589cc65d1d64bc172015588348feeffe
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/18340
Reviewed-by: David Neto <dneto@google.com>