Make NumberUnlocalizer aware of incomplete $separatorTransformTable

Very few (currently five) languages replace only one of the two
separator characters, e.g. by setting
$separatorTransformTable = array( ',' => ' ' );
instead of
$separatorTransformTable = array( ',' => ' ', '.' => '.' );
That's perfectly fine.

Code doing the inverse operation (unlocalizing) shouldn't rely on
the presence of both characters in the array keys. The canonical
characters should simply be hard coded ',' and '.'. There are no
constants for these as far as I can tell.

Same for $digitTransformTable if a language does not replace all
ten digits, e.g. $digitTransformTable = array( '0' => '?' );
We currently don't have a language that does that.

This problem does not occur at wikidata.org currently and probably
will not anyway since the parse API calls miss the "lang" option.

http://localhost/repowiki/api.php?action=wbparsevalue&format=json&parser=quantity&values=1.2&options={"lang":"la"}

Change-Id: I754fe953895212d190f40711cec4dd20f71aa19d
Merge "Make NumberUnlocalizer aware of incomplete $separatorTransformTable"