Introduce a new higher-order UDF that returns a new map by applying a
lambda `(k, v) -> expr` to each entry of the input map, transforming the
values while preserving the keys. Registered under the alias
`transform_values` via `with_aliases` from apache#22593.

Also fix a latent indexing bug in `LambdaExpr`: when a multi-parameter
lambda referenced only a subset of its declared parameters (e.g.
`(k, v) -> v * 2`), the compressed column index map could shift lambda
params into outer capture slots. `LambdaExpr` now tracks
`outer_columns_count` and remaps indices so outer captures and lambda
params keep stable positions regardless of which params are used.

Run `./dev/update_function_docs.sh` so the user-facing function
reference picks up the new `map_transform` entry from its
`#[user_doc(...)]` annotation.

Rename `map_transform` to `transform_values` (Spark/Trino spelling, leaves room
for a future `transform_keys`), extract shared helpers in this file and
`utils.rs` (`get_map_key_value_fields`, reuse `value_lambda_pair` from
`lambda_utils`), return an array of nulls (instead of a null scalar) when every
input row is null, and move the empty-entries fast path up next to the all-null
fast path. Also add a sqllogictest covering the all-null rows behavior and
regenerate the scalar function docs.

Adds four unit tests requested in PR review:
- `transform_values_empty_map`: single row, empty entries
- `transform_values_mixed_empty_null_populated_rows`: empty + null + populated
  rows in one batch to exercise offset/null-mask plumbing
- `transform_values_on_sliced_map_should_not_evaluate_on_unreachable_values`:
  slices a 4-row map and uses `100 / v` so a leading `0` would divide-by-zero
  if offset handling is wrong
- `transform_values_function_should_not_be_evaluated_on_values_underlying_null`
  (ignored): documents the dependency on apache#22847 which adds
  `clear_null_values` support for `MapArray`

While adding the empty-map test, the previously-existing "empty entries"
fast-path was found to be broken — `ScalarValue::new_default` for a `Map`
return type produces a scalar that decodes back as a `Struct`, not a `Map`,
and the test downcast failed. The fast path was just an optimisation skipping
the lambda evaluation; the regular path already handles empty inputs
correctly, so the buggy fast path was removed.

Per maintainer request on PR apache#22689, the `LambdaExpr::try_new` /
`expressions::lambda(...)` signature change (adding `outer_columns_count`)
is being reviewed separately in apache#22853 because it's a
breaking change to the physical-expr public API and warrants its own
attention, distinct from this additive UDF.

This commit reverts the `lambda.rs` / `higher_order_function.rs` /
`planner.rs` files to their `upstream/main` state, removes the
sqllogictest file (every query in it uses `(k, v) -> body` lambdas that
require the upstream fix), and marks the unit tests that exercise
multi-parameter lambdas with
`#[ignore = "blocked on apache#22853: multi-param lambda projection fix"]`.

`transform_values_uses_keys_via_case` and
`transform_values_all_null_rows_returns_null_array` still pass because
the former references both `k` and `v` (so projection is a no-op) and
the latter short-circuits before evaluating the lambda. This PR will be
rebased onto main once apache#22853 merges, at which point the ignore
markers will be removed and the sqllogictest file restored.