feat: add --location=<href> and globalThis.location (#7369)

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+## Location API
+
+Deno supports the
+[`location`](https://developer.mozilla.org/en-US/docs/Web/API/Window/location)
+global from the web. Please read on.
+
+### Location flag
+
+There is no "web page" whose URL we can use for a location in a Deno process. We
+instead allow users to emulate a document location by specifying one on the CLI
+using the `--location` flag. It can be a `http` or `https` URL.
+
+```ts
+// deno run --location https://example.com/path main.ts
+
+console.log(location.href);
+// "https://example.com/path"
+```
+
+You must pass `--location <href>` for this to work. If you don't, any access to
+the `location` global will throw an error.
+
+```ts
+// deno run main.ts
+
+console.log(location.href);
+// error: Uncaught ReferenceError: Access to "location", run again with --location <href>.
+```
+
+Setting `location` or any of its fields will normally cause navigation in
+browsers. This is not applicable in Deno, so it will throw in this situation.
+
+```ts
+// deno run --location https://example.com/path main.ts
+
+location.pathname = "./foo";
+// error: Uncaught NotSupportedError: Cannot set "location.pathname".
+```
+
+### Extended usage
+
+On the web, resource resolution (excluding modules) typically uses the value of
+`location.href` as the root on which to base any relative URLs. This affects
+some web APIs adopted by Deno.
+
+#### Fetch API
+
+```ts
+// deno run --location https://api.github.com/ --allow-net main.ts
+
+const response = await fetch("./orgs/denoland");
+// Fetches "https://api.github.com/orgs/denoland".
+```
+
+The `fetch()` call above would throw if the `--location` flag was not passed,
+since there is no web-analogous location to base it onto.
+
+#### Worker modules
+
+```ts
+// deno run --location https://example.com/index.html --allow-net main.ts
+
+const worker = new Worker("./workers/hello.ts", { type: "module" });
+// Fetches worker module at "https://example.com/workers/hello.ts".
+```
+
+### Only use if necessary
+
+For the above use cases, it is preferable to pass URLs in full rather than
+relying on `--location`. You can manually base a relative URL using the `URL`
+constructor if needed.
+
+The `--location` flag is intended for those who have some specific purpose in
+mind for emulating a document location and are aware that this will only work at
+application-level. However, you may also use it to silence errors from a
+dependency which is frivolously accessing the `location` global.