[SPARK-16839][SQL] Simplify Struct creation code path

## What changes were proposed in this pull request?

Simplify struct creation, especially the aspect of `CleanupAliases` which missed some aliases when handling trees created by `CreateStruct`.

This PR includes:

1. A failing test (create struct with nested aliases, some of the aliases survive `CleanupAliases`).
2. A fix that transforms `CreateStruct` into a `CreateNamedStruct` constructor, effectively eliminating `CreateStruct` from all expression trees.
3. A `NamePlaceHolder` used by `CreateStruct` when column names cannot be extracted from unresolved `NamedExpression`.
4. A new Analyzer rule that resolves `NamePlaceHolder` into a string literal once the `NamedExpression` is resolved.
5. `CleanupAliases` code was simplified as it no longer has to deal with `CreateStruct`'s top level columns.

## How was this patch tested?
Running all tests-suits in package org.apache.spark.sql, especially including the analysis suite, making sure added test initially fails, after applying suggested fix rerun the entire analysis package successfully.

Modified few tests that expected `CreateStruct` which is now transformed into `CreateNamedStruct`.

Author: eyal farago <eyal farago>
Author: Herman van Hovell <hvanhovell@databricks.com>
Author: eyal farago <eyal.farago@gmail.com>
Author: Eyal Farago <eyal.farago@actimize.com>
Author: Hyukjin Kwon <gurwls223@gmail.com>
Author: eyalfa <eyal.farago@gmail.com>

Closes #15718 from hvanhovell/SPARK-16839-2.

1 files changed, 6 insertions, 6 deletions

diff --git a/R/pkg/inst/tests/testthat/test_sparkSQL.R b/R/pkg/inst/tests/testthat/test_sparkSQL.R
index 806019d752..d7fe6b3282 100644
--- a/R/pkg/inst/tests/testthat/test_sparkSQL.R
+++ b/R/pkg/inst/tests/testthat/test_sparkSQL.R
@@ -1222,16 +1222,16 @@ test_that("column functions", {
   # Test struct()
   df <- createDataFrame(list(list(1L, 2L, 3L), list(4L, 5L, 6L)),
                         schema = c("a", "b", "c"))
-  result <- collect(select(df, struct("a", "c")))
+  result <- collect(select(df, alias(struct("a", "c"), "d")))
   expected <- data.frame(row.names = 1:2)
-  expected$"struct(a, c)" <- list(listToStruct(list(a = 1L, c = 3L)),
-                                 listToStruct(list(a = 4L, c = 6L)))
+  expected$"d" <- list(listToStruct(list(a = 1L, c = 3L)),
+                      listToStruct(list(a = 4L, c = 6L)))
   expect_equal(result, expected)
 
-  result <- collect(select(df, struct(df$a, df$b)))
+  result <- collect(select(df, alias(struct(df$a, df$b), "d")))
   expected <- data.frame(row.names = 1:2)
-  expected$"struct(a, b)" <- list(listToStruct(list(a = 1L, b = 2L)),
-                                 listToStruct(list(a = 4L, b = 5L)))
+  expected$"d" <- list(listToStruct(list(a = 1L, b = 2L)),
+                      listToStruct(list(a = 4L, b = 5L)))
   expect_equal(result, expected)
 
   # Test encode(), decode()