fix: document extension handling

[scolladon]

What does this pull request contains

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• Added for new features.
• Changed for changes in existing functionality.
• Deprecated for soon-to-be removed features.
• Removed for now removed features.
• Fixed for any bug fixes.
• Security in case of vulnerabilities.

Explain your changes

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Improve regex creating the document metadata members
Let it deals with the volatility of the extension based on the type of the file hosting the change (it can be either the file extension or the meta file)

Improve test for inFolder element
Improve assertion in test handler helper

Does this close any currently open issues?

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closes #135

• Jest test to check the fix is applied are added.

Where has this been tested?

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Operating System: Darwin Kernel Version 18.7.0: Tue Jan 12 22:04:47 PST 2021; root:xnu-4903.278.56~1/RELEASE_X86_64

yarn version: 1.22.10

node version: v14.16.0

git version: git version 2.31.1

sfdx version: sfdx-cli/7.98.0 darwin-x64 node-v14.16.0

sgd plugin version: sfdx-git-delta 4.4.0

[codecov]

Codecov Report

Merging #136 (03a16c0) into master (ae44c14) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #136   +/-   ##
=======================================
  Coverage   99.25%   99.25%           
=======================================
  Files          18       18           
  Lines         402      402           
=======================================
  Hits          399      399           
  Misses          3        3           

Impacted Files	Coverage Δ
src/service/inFolderHandler.js	100.00% <100.00%> (ø)

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