[IMP] core: reporting of browser logs / errors during setup

Sink handling of JS logging, exceptions and websocket timeouts so
calls other than _wait_code_ok handle them somewhat properly: the
issue fixed by odoo/odoo#41231 passed because it occurred during
module loading, which happens during initial page loading (browser_js
> navigate_to > _websocket_wait_event), which ignored logs (and
exceptions though here it's a console.error log), and as a result
reported no failure (and would simply miss that specific test as well
as every test following it).

Also since ChromeBrowser treats console.error as an exception,
important messages should be logged atomically. Merge two consecutive
console.error into a single one at the loading of modules so we don't
just get an exception "error while loading foo.bar" without any of the
useful details.

That ChromeBrowser treats console.error as exception is also why the
new method gets a flag (to suppress this behaviour): in the case of
two console.error, upon encountering the first it's treated as an
error so we try to take a screenshot, which goes through the messages
in order to get the screenshot response, which encounters the second
console.error, which gets treated as an exception, which hides the
first error.

Instead, screenshotting (and more generally _websocket_wait_id) should
treat console.error as a regular logging call, probably.

Also run JS tests in debug=assets for easier debugging (ha!) and
improve formatting of exception object when receiving an exception:
* if we can get a description on an `exception` remote object just
  print that, it's formatted to show the exception type, message &
  traceback
* otherwise format the garbage that is an "ExceptionDetails" object