Fix relative paths (#4594)

* Add tests for relativeRoot

* Remove path.posix.join

Since this is for file system paths it feels incorrect to use it on
URL paths as they are different in many ways.

* Rewrite cookie path logic

Before we relied on the client to resolve the base given to it by the
backend against the path.

Instead have the client pass that information along so we can resolve it
on the backend.  This means the client has to do less work.

* Do not remove out directory before watch

This is re-used for incremental compilation.

Also remove del since that was the only use (and we can use fs.rmdir in
the future if we need something like this).

* Remove unused function resolveBase

src/common/util.ts

@@ -23,6 +23,12 @@ export const generateUuid = (length = 24): string => {
 
 /**
  * Remove extra slashes in a URL.
+ *
+ * This is meant to fill the job of `path.join` so you can concatenate paths and
+ * then normalize out any extra slashes.
+ *
+ * If you are using `path.join` you do not need this but note that `path` is for
+ * file system paths, not URLs.
  */
 export const normalize = (url: string, keepTrailing = false): string => {
   return url.replace(/\/\/+/g, "/").replace(/\/+$/, keepTrailing ? "/" : "")
@@ -35,21 +41,6 @@ export const trimSlashes = (url: string): string => {
   return url.replace(/^\/+|\/+$/g, "")
 }
 
-/**
- * Resolve a relative base against the window location. This is used for
- * anything that doesn't work with a relative path.
- */
-export const resolveBase = (base?: string): string => {
-  // After resolving the base will either start with / or be an empty string.
-  if (!base || base.startsWith("/")) {
-    return base ?? ""
-  }
-  const parts = location.pathname.split("/")
-  parts[parts.length - 1] = base
-  const url = new URL(location.origin + "/" + parts.join("/"))
-  return normalize(url.pathname)
-}
-
 /**
  * Wrap the value in an array if it's not already an array. If the value is
  * undefined return an empty array.