Support EOF as statement separator in SQL scripts

Prior to Spring Framework 4.0.3, it was possible to supply a bogus
statement separator (i.e., a separator string that does not exist in
the configured SQL scripts) to ResourceDatabasePopulator with the side
effect that the entire contents of a script file would be interpreted
as a single SQL statement.

This undocumented feature was never intentional; however, some
developers came to rely on it. Unfortunately, changes made in
conjunction with SPR-9531 and SPR-11560 caused such scenarios to no
longer work.

This commit introduces first-class support for executing scripts which
contain a single statement that spans multiple lines but is not
followed by an explicit statement separator.

Specifically, ScriptUtils.EOF_STATEMENT_SEPARATOR may now be specified
as a 'virtual' statement separator to denote that a script contains a
single statement and no actual separator.

Issue: SPR-11687
(cherry picked from commit cc0ae3a881dde5910ecc340fa20c2365dd7474fa)
Make EOF_STATEMENT_SEPARATOR XML friendly

Changed the value of ScriptUtils.EOF_STATEMENT_SEPARATOR from
"<<< END OF SCRIPT >>>" to "^^^ END OF SCRIPT ^^^" so that the angle
brackets do not have to be escaped in XML configuration files.

Issue: SPR-11687
(cherry picked from commit 1753f5d1cab1b6b7226f3b655482dd43c111e94f)