Fix errors when running component server index

Passing an array to `path.join` is not supported, it takes unlimited
arguments rather than an array of one.

This was introduced in crrev.com/c/4678757, but I think the bots were
happy because they do not use the index page and instead navigate
directly to examples. This error only triggered on the index page.

As a drive-by, I also bumped the font size as otherwise they use the
default, rather small, DevTools font size.

Bug: none
Change-Id: I580c454d62e3ce66065bdb21c2fc7b0349825637
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/4685569
Reviewed-by: Andres Olivares <andoli@chromium.org>
Commit-Queue: Andres Olivares <andoli@chromium.org>
Auto-Submit: Jack Franklin <jacktfranklin@chromium.org>

front_end/ui/components/docs/component_docs_styles.css

@@ -35,6 +35,7 @@ body {
 
 .components-list a {
   display: block;
+  font-size: 14px;
   padding: 10px;
 }
 

scripts/component_server/server.js

@@ -156,7 +156,7 @@ function createComponentIndexFile(componentPath, componentExamples) {
 function createServerIndexFile(componentNames) {
   const linksToStyleSheets =
       styleSheetPaths
-          .map(link => `<link rel="stylesheet" href="${sharedResourcesBase}${path.join(link.split('/'))}" />`)
+          .map(link => `<link rel="stylesheet" href="${sharedResourcesBase}${path.join(...link.split('/'))}" />`)
           .join('\n');
 
   // clang-format off