[WIP]fix: show tables

[zxy-lgtm]

What this PR does:

Fix show tables errors, supports the same behavior as mysql.
ref: ttps://dev.mysql.com/doc/refman/8.0/en/show-tables.html

Which issue(s) this PR fixes:

Fixes #677

Special notes for your reviewer:

arana-db/parser#39

Does this PR introduce a user-facing change?:

[codecov-commenter]

Codecov Report

Patch coverage: 75.00% and project coverage change: +0.52% 🎉

Comparison is base (ca6a25c) 38.80% compared to head (518293a) 39.32%.

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #762      +/-   ##
==========================================
+ Coverage   38.80%   39.32%   +0.52%     
==========================================
  Files         259      259              
  Lines       26468    26812     +344     
==========================================
+ Hits        10271    10544     +273     
- Misses      15075    15135      +60     
- Partials     1122     1133      +11     

Files Changed	Coverage Δ
pkg/runtime/plan/dal/show_tables.go	0.00% <0.00%> (ø)
pkg/runtime/ast/show.go	37.23% <45.00%> (+7.62%)	⬆️
pkg/proto/rule/rule.go	59.72% <100.00%> (+8.93%)	⬆️
pkg/runtime/ast/ast.go	71.55% <100.00%> (+3.22%)	⬆️

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[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
2 Code Smells

No Coverage information
0.3% Duplication

[jjeffcaii]

It seems conflicts with the PR #761.