refactor(xsql): unify row and collection

[ngjaying]

• Each node now only needs to handle two kinds of data Row/Collection. Other data may be error, watermark, barrier

[codecov]

Codecov Report

Attention: Patch coverage is 74.34211% with 39 lines in your changes are missing coverage. Please review.

Project coverage is 63.48%. Comparing base (30bf65f) to head (b02c3a4).
Report is 1 commits behind head on master.

Files	Patch %	Lines
internal/topo/operator/project_operator.go	68.00%	5 Missing and 3 partials ⚠️
internal/xsql/collection.go	66.67%	8 Missing ⚠️
internal/topo/node/join_align_node.go	61.54%	4 Missing and 1 partial ⚠️
internal/topo/node/switch_node.go	50.00%	4 Missing and 1 partial ⚠️
internal/topo/operator/join_operator.go	66.67%	4 Missing ⚠️
internal/xsql/sorter.go	60.00%	3 Missing and 1 partial ⚠️
internal/topo/operator/analyticfuncs_operator.go	50.00%	2 Missing ⚠️
internal/topo/operator/func_operator.go	0.00%	2 Missing ⚠️
internal/topo/node/lookup_node.go	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2700      +/-   ##
==========================================
+ Coverage   63.46%   63.48%   +0.03%     
==========================================
  Files         337      338       +1     
  Lines       38899    38936      +37     
==========================================
+ Hits        24684    24718      +34     
- Misses      12050    12053       +3     
  Partials     2165     2165              

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