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.datasource.init.ScriptUtils. 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

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