Add lg-breakpoint margins & widths to support responsive in-app checkout design

In support of the work done for Update checkout page with registration shared l... (gitlab#352166 - closed)

Will add the following styles:

.gl-lg-mx-12 {
  @include media-breakpoint-up(lg) {
    margin-left: $gl-spacing-scale-12;
    margin-right: $gl-spacing-scale-12;
  }
}

.gl-lg-ml-12 {
  @include media-breakpoint-up(lg) {
    margin-left: $gl-spacing-scale-12;
  }
}

.gl-lg-mr-12 {
  @include media-breakpoint-up(lg) {
    margin-right: $gl-spacing-scale-12;
  }
}

.gl-lg-ml-10 {
  @include media-breakpoint-up(lg) {
    margin-left: $gl-spacing-scale-10;
  }
}

.gl-lg-mr-10 {
  @include media-breakpoint-up(lg) {
    margin-right: $gl-spacing-scale-10;
  }
}

.gl-lg-w-30p {
  @include gl-media-breakpoint-up(lg) {
    width: 30%;
  }
}

.gl-lg-w-40p {
  @include gl-media-breakpoint-up(lg) {
    width: 40%;
  }
}