### 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
var source = as(exchange.child(), LocalSourceExec.class);
        assertEquals(LocalSupplier.EMPTY, source.supplier());
    }
    /**
     * GrokExec[first_name{f}#4,Parser[pattern=%{WORD:b}.*, grok=org.elasticsearch.grok.Grok@60a20ab6],[b{r}#2]]
     * \_LimitExec[10000[INTEGER]]
     *   \_ExchangeExec[]
     *     \_ProjectExec[[_meta_field{f}#9, emp_no{f}#3, first_name{f}#4, gender{f}#5, languages{f}#6, last_name{f}#7, salary{f}#8]]
     *       \_FieldExtractExec[_meta_field{f}#9, emp_no{f}#3, first_name{f}#4, gen..]
     *         \_EsQueryExec[test], query[][_doc{f}#10], limit[10000], sort[] estimatedRowSize[216]
     */
    public void testGrok() {
        var plan = physicalPlan("""
            from test
            | grok first_name "%{WORD:b}.*"
            """);
        var optimized = optimizedPlan(plan);
        var grok = as(optimized, GrokExec.class);
        var limit = as(grok.child(), LimitExec.class);
        var exchange = asRemoteExchange(limit.child());
        var project = as(exchange.child(), ProjectExec.class);
        var extract = as(project.child(), FieldExtractExec.class);
        var source = source(extract.child());
        assertThat(source.estimatedRowSize(), equalTo(allFieldRowSize + Integer.BYTES + KEYWORD_EST));
    }
    public void testDissect() {
        var plan = physicalPlan("""
            from test
            | dissect first_name "%{b} "
            """);