Now that the `MemoryLayout` sealed hierarchy provides the same information, these redundant methods should be removed for reasons of consistency, symmetry, brevity and simplicity.

Here are the proposed replacements in user code:

layout.isPadding() -> layout instanceof PaddingLayout
layout.isUnion() -> layout instanceof UnionLayout
layout.isStruct() -> layout instanceof StructLayout

or in pattern matching:

switch (layout) {
    case PaddingLayout padding ->
    case UnionLayout union ->
    case StructLayout struct ->
    // more here
}

The proposed changes will affect the API which is in *preview*.