feat: browser_choose_file (#52)

Resolves https://github.com/microsoft/playwright-mcp/issues/31.

Prompt used for testing: 
```
upload test.txt to dropbox
```

This won't work for asynchronously opened filechoosers, but let's start
with the synchronous variant. I also tested with including the file
chooser open state in the snapshot, but that didn't give better results.

I also tested with OneDrive and WeTransfer, but somehow our ARIA
snapshots for those pages are missing some elements that are crucial to
locate the upload buttons.

src/index.ts

@@ -36,6 +36,7 @@ const snapshotTools: Tool[] = [
   common.navigate(true),
   common.goBack(true),
   common.goForward(true),
+  common.chooseFile(true),
   snapshot.snapshot,
   snapshot.click,
   snapshot.hover,
@@ -49,6 +50,7 @@ const screenshotTools: Tool[] = [
   common.navigate(false),
   common.goBack(false),
   common.goForward(false),
+  common.chooseFile(false),
   screenshot.screenshot,
   screenshot.moveMouse,
   screenshot.click,