Match non-anon struct literal syntax with anon

[bangseongbeom]

@andrewrk on #685 (comment) says that anonymous struct literal should be .{.field = value} instead of {.field = value} because it's like an anonymous enum literal, but for structs/unions.

Anonymous enum literal syntax is fairly seamless. It's just a removal of a type name. .bar is a removal of Foo in Foo.bar.

But this principle does not apply to anonymous struct literals. We need to add a new dot in front of curly braces after remove the type name. So Foo {.bar = 123} becomes .{.bar = 123}.

It may be worth to apply this 'non-anon to anon principle' to struct (and union, array). Like this:

	non-anonymous	anonymous
struct literal	Foo.{.bar = 123}	.{.bar = 123}
enum literal	Foo.bar	.bar

Or just remove . for struct literal only (this syntax is debated on #5039):

	non-anonymous	anonymous
struct literal	Foo {.bar = 123}	{.bar = 123}
enum literal	Foo.bar	.bar

[tauoverpi]

It may also be valuable to have a look at #5038 which would also solve this.

[Vexu]

Foo.{.bar = 123} was the syntax for a short period for another reason but was then reverted when a different solution was found because people didn't like that syntax: #760

[bangseongbeom]

Thanks for sharing the various syntax proposals! Helped me a lot.