fix: escaped string in GetOnDemand

[liuq19]

Main Changes:

1. fix the bugs when string has esacped chars in GetOnDemand
2. export the GetOnDemand API
3. reduce the repeated codes In different archs

[codecov-commenter]

Codecov Report

Merging #77 (5ee1acf) into master (4825b5e) will decrease coverage by 0.02%.
The diff coverage is 100.00%.

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@@            Coverage Diff             @@
##           master      #77      +/-   ##
==========================================
- Coverage   95.78%   95.77%   -0.02%     
==========================================
  Files          21       21              
  Lines        2445     2435      -10     
==========================================
- Hits         2342     2332      -10     
  Misses        103      103              

Impacted Files	Coverage Δ
include/sonic/error.h	100.00% <ø> (ø)
include/sonic/internal/arch/avx2/base.h	100.00% <ø> (ø)
include/sonic/internal/arch/avx2/unicode.h	100.00% <ø> (ø)
include/sonic/internal/arch/simd_skip.h	88.33% <ø> (-0.90%)	⬇️
include/sonic/dom/generic_document.h	95.60% <100.00%> (ø)
include/sonic/dom/parser.h	94.36% <100.00%> (+0.12%)	⬆️

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[liuq19]

Performace compare in x86:

Benchmark                                            Time             CPU      Time Old      Time New       CPU Old       CPU New
---------------------------------------------------------------------------------------------------------------------------------
twitter/SonicOnDemand_Normal                      -0.0024         -0.0044         25968         25906         25949         25834
citm_catalog/SonicOnDemand_Fronter                +0.0447         +0.0449         14726         15384         14717         15378
twitter/SonicOnDemand_NotFound                    +0.0104         +0.0103         25142         25403         25123         25382

[xiegx94]

LGTM