Which issue does this PR close?

Part of #21120 (framework + projection/filter integration)

Rationale for this change

DataFusion currently loses expression-level statistics when computing plan metadata. Projected expressions that aren't bare columns or literals get unknown statistics, and filter selectivity falls back to a hardcoded 20% when interval analysis cannot handle the predicate. There is also no extension point for users to provide statistics for their own UDFs.

This PR introduces ExpressionAnalyzer, a pluggable chain-of-responsibility framework that addresses these gaps. It follows the same extensibility pattern used elsewhere in DataFusion (ExprPlanner, OptimizerRule).

Addresses reviewer feedback from #19957: chain delegation, SessionState integration, own folder.

What changes are included in this PR?

• ExpressionAnalyzer trait with registry parameter for chain delegation
• ExpressionAnalyzerRegistry to chain analyzers (first Computed wins)
• DefaultExpressionAnalyzer: Selinger-style estimation for columns, literals, binary expressions (AND/OR/NOT/comparisons), arithmetic
• ExpressionAnalyzerRegistry stored in SessionState, injected into ProjectionExec and FilterExec by the planner
• ProjectionExprs uses registry to estimate NDV, min/max, and null fraction through projected expressions
• FilterExec uses registry selectivity as fallback when check_support returns false
• Config option optimizer.enable_expression_analyzer (default false) to opt in; zero behavior change when disabled
• Limitation: projections/filters created by optimizer rules after planning do not receive the registry and fall back to upstream behavior. Full coverage requires an operator-level statistics registry (orthogonal, will be tracked separately).

Are these changes tested?

• 15 unit tests for ExpressionAnalyzer (NDV, selectivity, min/max, null fraction, custom analyzers, chain delegation)
• 31 projection tests (including new test_project_statistics_with_expression_analyzer)
• 26 filter tests
• 7 session state tests

Are there any user-facing changes?

New public API (purely additive, non-breaking):

• ExpressionAnalyzer trait and ExpressionAnalyzerRegistry in datafusion-physical-expr
• SessionState::expression_analyzer_registry() getter
• SessionStateBuilder::with_expression_analyzer_registry() setter
• ProjectionExprs::with_expression_analyzer_registry() setter
• FilterExecBuilder::with_expression_analyzer_registry() setter
• ProjectionExec::with_expression_analyzer_registry() setter
• Config option datafusion.optimizer.enable_expression_analyzer

No breaking changes. Default behavior is unchanged (config defaults to false).

Disclaimer: I used AI to assist in the code generation, I have manually reviewed the output and it matches my intention and understanding.