### Description

Evals that introduce aliased can be simplified by extracting them into a project (and thus signaling there's no underlying processing).

The following eval:
`eval x = a + 1, y = x, z = y + 1, y = z, w = y + 1`
can be converted into:
`eval x = a + 1, z = a + 1 + 1, w = a + 1 + 1 | project x, z, z as y, w`

This helps fuse the project with other projections/aggs downstream.
x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/optimizer/PhysicalPlanOptimizerTests.java
*      \_ProjectExec[[_meta_field{f}#9, emp_no{f}#3, first_name{f}#4, !gender, languages{f}#6, last_name{f}#7, salary{f}#8]]
     *        \_FieldExtractExec[_meta_field{f}#9, first_name{f}#4, !gender, last_na..]
     *          \_LimitExec[10000[INTEGER]]
     *            \_FilterExec[NOT(emp_no{f}#3 == languages{f}#6)]
     *              \_FieldExtractExec[emp_no{f}#3, languages{f}#6]
     *                \_EsQueryExec[test], query[][_doc{f}#10], limit[], sort[]
     */
    public void testDontPushDownNegatedEqualityBetweenAttributes() {
        var plan = physicalPlan("""
            from test
            | where not emp_no == languages
            """);
        var optimized = optimizedPlan(plan);
        var topLimit = as(optimized, LimitExec.class);
        var exchange = asRemoteExchange(topLimit.child());
        var project = as(exchange.child(), ProjectExec.class);
        var extractRest = as(project.child(), FieldExtractExec.class);
        var localLimit = as(extractRest.child(), LimitExec.class);
        var filterExec = as(localLimit.child(), FilterExec.class);
        assertThat(filterExec.condition(), instanceOf(Not.class));
        var extractForFilter = as(filterExec.child(), FieldExtractExec.class);
        var source = source(extractForFilter.child());
        assertNull(source.query());
        assertThat(source.estimatedRowSize(), equalTo(allFieldRowSize + Integer.BYTES));
    }
    public void testEvalLike() {
        var plan = physicalPlan("""
            from test
            | eval x = concat(first_name, "--")
            | where x like "%foo%"