Modify the statement of index query to be consistent with standard SQL

[kr11]

1. change involved code in query processing package.
2. refine the test code of KVIndex.
3. change involved lines of TSParser.g.
4. Note that, Index query is conflict with Aggregation statement for the sake of LL principle(?). In this pull request, therefore, KVIndex is a constant. If we tend to add more index function in future, we have to change this part of Antlr grammar.

[MyXOF]

QP部分需要针对index增加相应的单元测试

[kr11]

@MyXOF test has been added.

[codecov[bot]]

Codecov Report

:exclamation: No coverage uploaded for pull request base (master@94af8f0). Click here to learn what that means. The diff coverage is 71.15%.

@@            Coverage Diff            @@
##             master     #249   +/-   ##
=========================================
  Coverage          ?   52.92%           
=========================================
  Files             ?      224           
  Lines             ?    26166           
  Branches          ?     7862           
=========================================
  Hits              ?    13849           
  Misses            ?    10749           
  Partials          ?     1568

Impacted Files	Coverage Δ
...ghua/iotdb/index/common/IndexManagerException.java	0% <ø> (ø)
...edu/tsinghua/iotdb/index/kvmatch/KvMatchIndex.java	0% <ø> (ø)
.../java/cn/edu/tsinghua/iotdb/qp/QueryProcessor.java	95.77% <ø> (ø)
...ghua/iotdb/qp/logical/crud/IndexQueryOperator.java	0% <0%> (ø)
.../tsinghua/iotdb/qp/logical/crud/IndexOperator.java	100% <100%> (ø)
...ua/iotdb/qp/exception/QueryProcessorException.java	100% <100%> (ø)
...edu/tsinghua/iotdb/qp/physical/crud/IndexPlan.java	70.37% <100%> (ø)
...java/cn/edu/tsinghua/iotdb/index/IndexManager.java	36.36% <50%> (ø)
.../tsinghua/iotdb/qp/strategy/PhysicalGenerator.java	71.22% <66.66%> (ø)
...tdb/qp/strategy/optimizer/ConcatPathOptimizer.java	77.01% <69.23%> (ø)
... and 1 more

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