to_number() - deferred features

Some features were not implemented in to_number() under terms of MDEV-20022:

• The ON CONVERSION ERROR clause
• The third parameter (nlsparam)
• Internationalized components: G, D, C, L, U.

Under terms of this task we'll implement these features.

The internationalized components need some new information to be added into sql_locale.cc first.
We do have information for group separators (G) and decimal delimiters (D).
But we don't need information about:

• C - the ISO currency symbol
• L - the local currency symbol
• U - the dual currency symbol (e.g. Euro)

So this information should be added first