std.builtin: rename Type.UnionField and Type.StructField's field_type to type

test/behavior/bugs/12786.zig

@@ -8,7 +8,7 @@ fn NamespacedGlobals(comptime modules: anytype) type {
             .fields = &.{
                 .{
                     .name = "globals",
-                    .field_type = modules.mach.globals,
+                    .type = modules.mach.globals,
                     .default_value = null,
                     .is_comptime = false,
                     .alignment = @alignOf(modules.mach.globals),

test/behavior/bugs/12794.zig

@@ -7,7 +7,7 @@ fn NamespacedComponents(comptime modules: anytype) type {
             .is_tuple = false,
             .fields = &.{.{
                 .name = "components",
-                .field_type = @TypeOf(modules.components),
+                .type = @TypeOf(modules.components),
                 .default_value = null,
                 .is_comptime = false,
                 .alignment = @alignOf(@TypeOf(modules.components)),

test/behavior/bugs/13435.zig

@@ -8,7 +8,7 @@ fn CreateUnion(comptime T: type) type {
             .fields = &[_]std.builtin.Type.UnionField{
                 .{
                     .name = "field",
-                    .field_type = T,
+                    .type = T,
                     .alignment = @alignOf(T),
                 },
             },

test/behavior/bugs/6456.zig

@@ -23,7 +23,7 @@ test "issue 6456" {
             fields = fields ++ &[_]StructField{StructField{
                 .alignment = 0,
                 .name = name,
-                .field_type = usize,
+                .type = usize,
                 .default_value = &@as(?usize, null),
                 .is_comptime = false,
             }};