1476: Support double-byte chars for LEFT(),RIGHT(), LEN() and MID().

[FlowingSPDG]

PR Details

Support double-byte characters support for string functions such as LEFT().

Description

Added double bytes chars support by using utf counting.

Related Issue

#1476

Motivation and Context

I was using Excel sheet that has Japanese characters in it, but those formulas were not supported at the moment,

How Has This Been Tested

Added testing

Types of changes

• Docs change / refactoring / dependency upgrade
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[FlowingSPDG]

I will add more tests for those functions if needed.
perhaps LEFTB/RIGHTB/MIDB should use current code since it counts bytes instead of text length.

[codecov-commenter]

Codecov Report

Merging #1477 (24669ba) into master (cb0c1b0) will not change coverage.
The diff coverage is 100.00%.

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@@           Coverage Diff           @@
##           master    #1477   +/-   ##
=======================================
  Coverage   98.68%   98.68%           
=======================================
  Files          31       31           
  Lines       24274    24274           
=======================================
  Hits        23956    23956           
  Misses        210      210           
  Partials      108      108           

Flag	Coverage Δ
unittests	98.68% <100.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
calc.go	99.03% <100.00%> (ø)

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[xuri]

LGTM, thanks for your contribution.

[FlowingSPDG]

Thank you for quick response! I have added some testing and xxxB(LENB/RIGHTB/MIDB) function code so let me make PR again.