resourceloader: Use 'enableModuleContentVersion' for startup module

resourceloader: Use 'enableModuleContentVersion' for startup module

This significantly simplifies the getVersionHash implementation for
StartupModule, and fixes a couple of bugs.

Previously, the startup module's E-Tag was determined by the
'getDefinitionSummary' method, which combined the E-Tag values
from all registered modules, plus what we thought is all information
used by 'getScript' (config vars, embedded script files, list
of base modules, ...)

However, this were various things part of the manifest that it
forgot about, including:

* Changes to the list of dependencies of a module.
* Changes to the name of module.
* Changes to the cache group of module.
* Adding or removing a foreign module source (mw.loader.addSource).

These are all quite rare, and when they do change, they usually
also involve a change that *was* tracked already. But, sometimes
they don't and that's when bugs happened.

Instead of the tracking array of getDefinitionSummary, we now
use the 'enableModuleContentVersion' option for StartupModule,
which simply calls the actual getScript() method and hashes that.

Of note: When an exception happens with the version computation of
any individual module, we catch it, log it, and continue with the
rest. Previously, the first time such error was discovered at
run-time would be in the getCombinedVersion() call from
StartupModule::getAllModuleHashes(). That public getCombinedVersion()
method of ResourceLoader had the benefit of also outputting details
of that exception in the HTTP response output. In order to keep that
behaviour, I made outputErrorAndLog() public so that StartupModule
can call it directly now. This is covered by
ResourceLoaderTest::testMakeModuleResponseStartupError.

Bug: T201686
Change-Id: I8e8d3a2cd2ccd68d2d78e988bcdd0d77fbcbf1d4