JX Browser setup: failed to extract chromium binaries

In trying to initialize JX browser, an exception was thrown here: https://github.com/flutter/flutter-intellij/blob/8a864aa1665b80805ba9094bf3e58ae9f220792c/flutter-idea/src/io/flutter/jxbrowser/EmbeddedBrowserEngine.java#L49

Because the exception is swallowed, we were setting `engine` to null here: https://github.com/flutter/flutter-intellij/blob/8a864aa1665b80805ba9094bf3e58ae9f220792c/flutter-idea/src/io/flutter/jxbrowser/EmbeddedBrowserEngine.java#L53

We should not be swallowing this exception, because this left JX browser in an unrecoverable state. The solution was to delete the directory that JX Browser was trying to be extracted in `rm -rf var/folders/vq/0jb4fqyn6_q03n58xhr8yq4800fv4z/T/JxBrowser/`. I only knew this path from the exception thrown above, but this information would not normally be passed along to the end user. We should recover from this state, perhaps adding a button to delete the cache and try again, essentially automating the steps I had to perform manually.