Bug#36353447 No public symbol mysql::collation::find_by_id()

Include the mysql::collation namespace in the implementation of
find_by_id(). Add a find_by_id() test to libstrings_shared-t
and libstrings_static-t.

Change-Id: Ifdae1e2a208d9846d8968e9323c7f21c59340014

Author: jdduncan

strings/collations.cc

@@ -113,7 +113,9 @@ const CHARSET_INFO *mysql::collation::find_by_name(const Name &name) {
   return entry()->find_by_name(name);
 }
 
-const CHARSET_INFO *find_by_id(unsigned id) { return entry()->find_by_id(id); }
+const CHARSET_INFO *mysql::collation::find_by_id(unsigned id) {
+  return entry()->find_by_id(id);
+}
 
 const CHARSET_INFO *mysql::collation::find_primary(Name cs_name) {
   // Needed by lexer, to parse e.g. "select _utf8 0xD0B0D0B1D0B2;"

unittest/examples/libstrings-t.cc

@@ -47,6 +47,8 @@ int main() {
       mysql::collation::find_by_name("utf8mb4_zh_0900_as_cs");
   std::cout << "Ok: " << zh_cs->csname << " " << zh_cs->m_coll_name
             << std::endl;
+  const CHARSET_INFO *cs_id = mysql::collation::find_by_id(cs->number);
+  std::cout << "OK: " << cs_id->csname << " " << cs_id->number << std::endl;
   mysql::collation::shutdown();
   return 0;
 }