Inherit table charset/collation from db charset

This reverts commit e3ab1276, reversing
changes made to f988b0a6.

People that are starting a new project will immediately know what this
is about, but people upgrading doctrine might get a lot of these and
should have a better clue regarding what this is about.

People do not need to know that this will be implemented as an
exception.

I am not sure if there is a rationale behind ignoring extra keys like
this. I was under the impression that something might copy options to
platform specific options, thus leaving options in the original array,
knowing they would be ignored anyway. If it is the case, it would be
best to just move them, otherwise, this commit might help troubleshoot
some mapping issues.
I had to fix some tests that wrongly used that options array (maybe
these options were valid at some point?).

The reasoning behind this is to essentially rely on a single type (or
the absence of it), therefore add type declarations.

Since these are private methods we can do that without breaking BC.

Unescaping re-added, support limited to schema introspection (#2850 will bring more complete coverage)

@morozov review: According to MySqlPlatform::getListTableColumnsSQL(), the default column is always selected. Removed ??