Optimize ShardingTableBroadcastRoutingEngine and SingleTableSQLRouter logic for PostgreSQL schema

[strongduanmu]

Ref #14004.

Changes proposed in this pull request:

• optimize ShardingTableBroadcastRoutingEngine logic for PostgreSQL schema
• optimize SingleTableSQLRouter logic for PostgreSQL schema
• modify unit test

[codecov-commenter]

Codecov Report

Merging #17155 (5e252d5) into master (6533e51) will increase coverage by 0.11%.
The diff coverage is 39.13%.

@@             Coverage Diff              @@
##             master   #17155      +/-   ##
============================================
+ Coverage     60.26%   60.38%   +0.11%     
- Complexity     2114     2115       +1     
============================================
  Files          3490     3492       +2     
  Lines         52192    52213      +21     
  Branches       8883     8889       +6     
============================================
+ Hits          31456    31530      +74     
+ Misses        18100    18038      -62     
- Partials       2636     2645       +9     

Impacted Files	Coverage Δ
...resher/type/DropIndexStatementSchemaRefresher.java	13.63% <0.00%> (+3.95%)	⬆️
...sphere/singletable/route/SingleTableSQLRouter.java	62.06% <50.00%> (ø)
.../route/engine/type/ShardingRouteEngineFactory.java	68.67% <100.00%> (+0.43%)	⬆️
...broadcast/ShardingTableBroadcastRoutingEngine.java	68.00% <100.00%> (+0.65%)	⬆️
.../infra/metadata/schema/util/IndexMetaDataUtil.java	80.00% <100.00%> (+2.22%)	⬆️
...est/column/value/impl/MySQLUnsignedIntHandler.java	66.66% <0.00%> (-33.34%)	⬇️
...column/value/impl/MySQLUnsignedTinyintHandler.java	66.66% <0.00%> (-33.34%)	⬇️
...olumn/value/impl/MySQLUnsignedSmallintHandler.java	66.66% <0.00%> (-33.34%)	⬇️
...lumn/value/impl/MySQLUnsignedMediumintHandler.java	66.66% <0.00%> (-33.34%)	⬇️
.../column/value/impl/MySQLUnsignedBigintHandler.java	71.42% <0.00%> (-28.58%)	⬇️
... and 20 more

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