issue: 2607- added support for MapFromEntries

[athlcode]

Which issue does this PR close?

Closes #2706.

Rationale for this change

Comet already delegated MapFromEntries to the upstream datafusion-spark UDF, but the docs still listed it as unsupported and the native path silently collapsed duplicate keys — diverging from Spark's default spark.sql.mapKeyDedupPolicy=EXCEPTION. Paired with the companion datafusion PR (which makes the native UDF raise [DUPLICATED_MAP_KEY] on duplicates).

What changes are included in this PR?

1. Flip map_from_entries to supported in docs/spark_expressions_support.md.
2. In maps.scala, add a guard in CometMapFromEntries.getSupportLevel that returns Incompatible when spark.sql.mapKeyDedupPolicy is not EXCEPTION, so LAST_WIN queries fall back to Spark. Binary key/value fallbacks are unchanged.

How are these changes tested?

One new test in CometMapExpressionSuite.scala:

map_from_entries - duplicate keys throw under default EXCEPTION policy — asserts the native path surfaces DUPLICATED_MAP_KEY, confirming error-class parity with Spark.

[coderfender]

@athlcode , you might want to wait till the PR on DF's side is merged and released before adding support on comet :
apache/datafusion#21720

[coderfender]

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