fix(docs-infra): improve line-spacing between search results (esp. for wrapped lines) (#40802)

Previously, the line-spacing between different search result items was
the same as that between wrapped lines of the same result. This made it
difficult to distinguish the different results.

This commit fixes it by reducing the line-spacing between wrapped lines
of the same result item and keeping a larger line-spacing between
different results.

Before: ![search-results before][1]
After: ![search-results after][2]

[1]: https://user-images.githubusercontent.com/8604205/107229685-ca48c400-6a26-11eb-8161-0c0768b10a2d.png
[2]: https://user-images.githubusercontent.com/8604205/107229691-ccab1e00-6a26-11eb-9594-d4c37d0d72b2.png

PR Close #40802

aio/src/styles/2-modules/_search-results.scss

@@ -41,8 +41,11 @@ aio-search-results {
 
         .search-result-item {
           @include font-size(14);
+          @include line-height(24);
           color: $lightgray;
+          display: inline-block;
           font-weight: normal;
+          padding: 0.6rem 0;
 
           &a {
             text-decoration: none;