docs: compact the API Reference links (#21285)

This PR is opinionated. 
Issue: the `API Reference` sections in the examples hold too much
vertical space and make us scroll the page too much. See an
[example](https://python.langchain.com/docs/get_started/quickstart/#conversation-retrieval-chain).
These sections are **important**. So, the compacting should not make
these sections less noticeable.
Change: compacting the `API Reference` sections. See the [same example
after change
applied](https://langchain-j6nya46lf-langchain.vercel.app/docs/get_started/quickstart/#conversation-retrieval-chain).
It is more compact and now looks like references (footnotes).
Note: I would also change the section style, so it would be more
noticeable (maybe to look like the footnotes. Smaller wider font?)

---------

Co-authored-by: Bagatur <22008038+baskaryan@users.noreply.github.com>
Co-authored-by: Bagatur <baskaryan@gmail.com>

docs/src/theme/CodeBlock/index.js

@@ -16,18 +16,14 @@ function Imports({ imports }) {
         borderBottomRightRadius: "var(--ifm-code-border-radius)",
       }}
     >
-      <h4 style={{ paddingLeft: "0.65rem", marginBottom: "0.45rem" }}>
+      <b style={{ paddingLeft: "0.65rem", marginBottom: "0.45rem", marginRight: "0.5rem" }}>
         API Reference:
-      </h4>
-      <ul style={{ paddingBottom: "1rem" }}>
-        {imports.map(({ imported, source, docs }) => (
-          <li key={imported}>
-            <a href={docs}>
-              <span>{imported}</span>
-            </a>
-          </li>
+      </b>
+        {imports.map(({ imported, source, docs }, index) => (
+          <span key={imported}>
+            <a href={docs}>{imported}</a>{index < imports.length - 1 ? ' | ' : ''}
+          </span>
         ))}
-      </ul>
     </div>
   );
 }