fix extra spaces in if-expr with bool negation

[tjhance]

Currently, verusfmt adds a space for each 'condition' node. However, the grammar is set up so that this has two condition nodes:

if !b {
}

so it ends up formatted as:

if !b  {
}

See the expansion has two 'condition' nodes:

if_expr {
                  if_str {}
                  condition {
                    bang_str {}
                    condition {
                      expr_no_struct {
                        path_expr_no_generics {
                          path_no_generics {
                            path_segment_no_generics {
                              name_ref {
                                identifier {}
                              }
                            }
                          }
                        }
                      }
                    }
                  }

The PR changes the handling of the space to be with an 'if' expression or 'while' expression, rather than having it handled with the 'condition' node.

[parno]

Looks nice -- thanks for the fix!