parser: add explain format for optimizer trace

[winoros]

What problem does this PR solve?

Add one more new explain format to enable optimizer trace.

Check List

Tests

• Unit test

[codecov[bot]]

Codecov Report

Merging #684 into master will increase coverage by <.01%. The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #684      +/-   ##
==========================================
+ Coverage   79.82%   79.82%   +<.01%     
==========================================
  Files          37       37              
  Lines       13625    13635      +10     
==========================================
+ Hits        10876    10884       +8     
- Misses       2103     2105       +2     
  Partials      646      646

Impacted Files	Coverage Δ
parser.go	93.13% <ø> (-0.03%)	:arrow_down:
ast/misc.go	76.14% <ø> (ø)	:arrow_up:
misc.go	93.49% <ø> (ø)	:arrow_up:

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[ti-chi-bot]

@winoros: PR needs rebase.

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