fix(dateFilter): ignore era format specifier "G"

The era format specifier is not supported in our locale code and is being
passed through as the letter G in some long date formats, such as Thai (th-th).

It is not straightforward to provide locale specific era formatting since
the logic is calendar (locale) specific and not provided by the Google
closure library.

This commit simply ignores the G in format strings until we can work out
a better strategy for dealing with eras.

Closes #10503