stage2: fixups for topolarity-comptime-memory-reinterp branch

* don't store `has_well_defined_layout` in memory.
 * remove struct `hasWellDefinedLayout` logic. it's just
   `layout != .Auto`. This means we only need one implementation, in
   Type.
 * fix some of the cases being wrong in `hasWellDefinedLayout`, such as
   optional pointers.
 * move `tag_ty_inferred` field into a position that makes it more
   obvious how the struct layout will be done. Also we don't have a
   compiler that intelligently moves fields around so this layout is
   better.
 * Sema: don't `resolveTypeLayout` in `zirCoerceResultPtr` unless
   necessary.
 * Rename `ComptimePtrLoadKit` `target` field to `pointee` to avoid
   confusion with `target`.

src/Module.zig

@@ -885,7 +885,6 @@ pub const Struct = struct {
     /// one possible value.
     known_non_opv: bool,
     requires_comptime: PropertyBoolean = .unknown,
-    has_well_defined_layout: PropertyBoolean = .unknown,
 
     pub const Fields = std.StringArrayHashMapUnmanaged(Field);
 
@@ -1080,8 +1079,6 @@ pub const EnumFull = struct {
     /// An integer type which is used for the numerical value of the enum.
     /// Whether zig chooses this type or the user specifies it, it is stored here.
     tag_ty: Type,
-    /// true if zig inferred this tag type, false if user specified it
-    tag_ty_inferred: bool,
     /// Set of field names in declaration order.
     fields: NameMap,
     /// Maps integer tag value to field index.
@@ -1092,6 +1089,8 @@ pub const EnumFull = struct {
     namespace: Namespace,
     /// Offset from `owner_decl`, points to the enum decl AST node.
     node_offset: i32,
+    /// true if zig inferred this tag type, false if user specified it
+    tag_ty_inferred: bool,
 
     pub const NameMap = std.StringArrayHashMapUnmanaged(void);
     pub const ValueMap = std.ArrayHashMapUnmanaged(Value, void, Value.ArrayHashContext, false);
@@ -1136,7 +1135,6 @@ pub const Union = struct {
         fully_resolved,
     },
     requires_comptime: PropertyBoolean = .unknown,
-    has_well_defined_layout: PropertyBoolean = .unknown,
 
     pub const Field = struct {
         /// undefined until `status` is `have_field_types` or `have_layout`.