initial expression tree validation logic

[alex-dukhno]

linked with #598

[coveralls]

Pull Request Test Coverage Report for Build 912154682

• 374 of 637 (58.71%) changed or added relevant lines in 26 files are covered.
• 5 unchanged lines in 3 files lost coverage.
• Overall coverage decreased (-1.5%) to 66.451%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
sql_engine/catalog/src/lib.rs	4	5	80.0%
sql_engine/data_definition/execution_plan/src/lib.rs	0	1	0.0%
data_repr/scalar/src/lib.rs	4	8	50.0%
expression_validator/src/lib.rs	41	45	91.11%
node_engine/src/transaction_manager.rs	2	6	33.33%
sql_engine/query_processing/type_inference/src/lib.rs	15	24	62.5%
inter_repr/typed_tree/src/lib.rs	14	26	53.85%
sql_engine/data_manipulation/untyped_tree_old/src/lib.rs	0	14	0.0%
inter_repr/untyped_tree/src/lib.rs	7	22	31.82%
sql_engine/data_manipulation/typed_tree_old/src/lib.rs	29	48	60.42%
<!--	Total:	374	637	58.71%	-->

Files with Coverage Reduction	New Missed Lines	%
data_repr/scalar/src/lib.rs	1	51.72%
sql_engine/data_definition/execution_plan/src/lib.rs	1	64.71%
types/src/lib.rs	3	65.12%
<!--	Total:	5		-->

Totals
Change from base Build 877821299:	-1.5%
Covered Lines:	2460
Relevant Lines:	3702

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💛 - Coveralls