expand paren rules for default rendering, sqlite/mysql

expand paren rules for default rendering, sqlite/mysql

Expanded the rules for when to apply parenthesis to a server default in DDL
to suit the general case of a default string that contains non-word
characters such as spaces or operators and is not a string literal.

Fixed issue in MySQL server default reflection where a default that has
spaces would not be correctly reflected.  Additionally, expanded the rules
for when to apply parenthesis to a server default in DDL to suit the
general case of a default string that contains non-word characters such as
spaces or operators and is not a string literal.

Fixes: #12425
Change-Id: Ie40703dcd5fdc135025d676c01baba57ff3b71ad