Implement json visitor for plan node

[longjiquan]

/kind improvement

[codecov]

Codecov Report

Merging #22897 (1e3882a) into sql_beta (348fba4) will increase coverage by 0.21%.
The diff coverage is 97.81%.

@@             Coverage Diff              @@
##           sql_beta   #22897      +/-   ##
============================================
+ Coverage     81.64%   81.85%   +0.21%     
============================================
  Files           771      776       +5     
  Lines         99924   100230     +306     
============================================
+ Hits          81586    82048     +462     
+ Misses        15217    15068     -149     
+ Partials       3121     3114       -7     

Impacted Files	Coverage Δ
internal/mysqld/parser/antlrparser/node_ret.go	43.68% <ø> (-3.27%)	⬇️
...mysqld/planner/visitor_expression_text_restorer.go	44.08% <ø> (ø)
internal/mysqld/planner/test_value.go	50.00% <50.00%> (ø)
...ld/parser/antlrparser/node_ret_wrong_var_naming.go	75.00% <75.00%> (ø)
internal/mysqld/parser/antlrparser/ast_builder.go	38.29% <100.00%> (ø)
internal/mysqld/planner/node_equal.go	100.00% <100.00%> (ø)
internal/mysqld/planner/sql_statements.go	100.00% <100.00%> (+13.33%)	⬆️
internal/mysqld/planner/visitor_json.go	100.00% <100.00%> (ø)
...al/mysqld/planner/visitor_json_wrong_var_naming.go	100.00% <100.00%> (ø)

... and 45 files with indirect coverage changes

[czs007]

/approve
/lgtm

[sre-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: czs007, longjiquan

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