Lexical ordering of strings with surrogate pairs

[dlurton]

Description

PartiQL can get the ordering of strings wrong if they contain surrogate pairs.

To Reproduce

This is a somewhat contrived example, but it demonstrates the point.

@Test
fun `lexical ordering of strings with surrogate pairs`() {
    // The codepoint of 'ꬰ' is U+AB30.
    // The codepoint of `💩` is U+1F4A9.
    // Therefore, `ꬰ` should be ordered first by PartiQL.

    // However, PartiQL currently falls back on the JVM to compare strings.  The JVM lexicographcailly
    // compares by UTF-16 code unit instead of full code point and this can cause strings with characters
    // requiring surrogate pairs to sort incorrectly.
    
    // Therefore this test fails.

    assertTrue(
        DEFAULT_COMPARATOR.compare(
            ExprValue.newString("ꬰ"),
            ExprValue.newString("💩")
        ) > 0,
        "'ꬰ' should come before '💩'"
    )
}

Expected Behavior

The test in the repro case should pass.

Additional Context

I can't think of anything else to add.