feat(func): add rule_start()

[ngjaying]

Closes #2040

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.02% 🎉

Comparison is base (9f11f4d) 61.62% compared to head (f1ca5e7) 61.64%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2143      +/-   ##
==========================================
+ Coverage   61.62%   61.64%   +0.02%     
==========================================
  Files         282      282              
  Lines       33389    33395       +6     
==========================================
+ Hits        20573    20584      +11     
+ Misses      10874    10869       -5     
  Partials     1942     1942              

Files Changed	Coverage Δ
internal/topo/context/default.go	87.34% <ø> (ø)
internal/binder/function/funcs_misc.go	68.88% <100.00%> (+0.29%)	⬆️
internal/topo/topo.go	93.33% <100.00%> (+0.04%)	⬆️

... and 2 files with indirect coverage changes

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