Add multi line SQL comment support

Prior to this commit neither
org.springframework.jdbc.datasource.init.ResourceDatabasePopulator nor
org.springframework.test.jdbc.JdbcTestUtils properly supported C-style
block comments "/*...*/". Secondarily there had developed a significant
amount of duplicate code in the two classes that could lead to future
maintenance issues.

This commit consolidates the duplicate code from the two classes into
org.springframework.jdbc.support.JdbcUtils. Relevant test cases have
also been migrated. It also contains a modification to the
splitSqlScript() method so that the C-style block comments are now
removed from the script during processing. A new test case was added for
the new multi line comment support.

Issue: SPR-9531