bsn: support inline macros in field value position

[cart]

Objective

bsn! currently requires surrounding macros in "field value position" with {}:

bsn! {
  Foo { value: {vec![ 100, 200 ]} }
}

This is annoying!

Solution

Support macros in field-value-position:

bsn! {
  Foo { value: vec![ 100, 200 ] }
}

Testing

• Added a test that checks that this works
• Ported bsn! examples to use this

[laundmo]

This should be added to docs (at least the syntax table) once #24464 is merged