### 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/LogicalPlanOptimizerTests.java
"y",
                    new Mul(EMPTY, new FieldAttribute(EMPTY, "emp_no", mapping.get("emp_no")), new Literal(EMPTY, 2, INTEGER))
                )
            )
        );
    }
    public void testPushDownDissectPastProject() {
        LogicalPlan plan = optimizedPlan("""
            from test
            | rename first_name as x
            | keep x
            | dissect x "%{y}"
            """);
        var keep = as(plan, Project.class);
        var dissect = as(keep.child(), Dissect.class);
        assertThat(dissect.extractedFields(), contains(new ReferenceAttribute(Source.EMPTY, "y", DataTypes.KEYWORD)));
    }
    public void testPushDownGrokPastProject() {
        LogicalPlan plan = optimizedPlan("""
            from test
            | rename first_name as x
            | keep x
            | grok x "%{WORD:y}"
            """);
        var keep = as(plan, Project.class);
        var grok = as(keep.child(), Grok.class);
        assertThat(grok.extractedFields(), contains(new ReferenceAttribute(Source.EMPTY, "y", DataTypes.KEYWORD)));
    }
    public void testPushDownFilterPastProjectUsingEval() {
        LogicalPlan plan = optimizedPlan("""