Change all console.errors to console.warns

[nolanlawson]

People commonly see "errors" like this:

Error: [LWC error]: The `appendChild` method is available only on elements that use the `lwc:dom="manual"` directive.

... and they assume this is related to some other error. In fact, it's basically a warning, because we continue rendering regardless. But because it's red, it looks like an error.

We should replace all logError calls with logWarn. If we're going to log something and not throw an Error, then the text should be yellow rather than red.