refactor: reduce imports for react-sytax-highlighter

[efloden]

JIRA issue URL: N/A

Reduces the import footprint of the react-syntax-highlighter significantly by only importing the xml language. (which is all we are using at the moment)

Checklist

• JIRA link
• Check target branch
• Make sure all commit statuses are green or otherwise documented reasons to ignore
• QA needs to evaluate against the JIRA ticket
• Changed files and commits make sense for this PR

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This change is 

[alex-sl-eng]

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Reviewed 1 of 1 files at r1.
Review status: all files reviewed at latest revision, all discussions resolved, some commit checks broke.

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Comments from Reviewable

[alex-sl-eng]

@efloden please check the failed jenkins build.

[codecov]

Codecov Report

Merging #665 into master will increase coverage by 0.06%.
The diff coverage is 100%.

@@             Coverage Diff              @@
##             master     #665      +/-   ##
============================================
+ Coverage     33.14%    33.2%   +0.06%     
- Complexity     5775    11568    +5793     
============================================
  Files          1575     3152    +1577     
  Lines         62267   124752   +62485     
  Branches       7351    14745    +7394     
============================================
+ Hits          20638    41425   +20787     
- Misses        39706    79454   +39748     
- Partials       1923     3873    +1950

Impacted Files	Coverage Δ	Complexity Δ
...app/editor/components/TransUnitTranslationPanel.js	13.88% <100%> (+13.88%)	0 <0> (ø)	⬇️
...ain/java/org/zanata/rest/review/ReviewService.java	72% <0%> (-12.22%)	7% <0%> (+1%)
...n-util/src/main/java/org/zanata/util/HashUtil.java	73.68% <0%> (-4.1%)	7% <0%> (ø)
...va/org/zanata/util/SynchronizationInterceptor.java	68.42% <0%> (-3.81%)	3% <0%> (ø)
...ta-model/src/main/java/org/zanata/tmx/TMXUtil.java	82.5% <0%> (-2.12%)	17% <0%> (ø)
...va/org/zanata/search/AbstractIndexingStrategy.java	56.66% <0%> (-1.96%)	5% <0%> (ø)
.../main/java/org/zanata/util/CommonMarkRenderer.java	76.19% <0%> (-1.86%)	6% <0%> (ø)
...zanata/search/HTextFlowTargetIndexingStrategy.java	68.29% <0%> (-1.71%)	7% <0%> (ø)
...ontend/src/app/editor/reducers/settings-reducer.js	90.19% <0%> (-1.48%)	0% <0%> (ø)
.../java/org/zanata/rest/client/TraceDebugFilter.java	77.77% <0%> (-1.47%)	12% <0%> (ø)
... and 1665 more

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[efloden]

@aeng build passing now

[alex-sl-eng]

@efloden probably its a good idea to increase the test coverage for this component.

[alex-sl-eng]

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Reviewed 2 of 2 files at r2.
Review status: all files reviewed at latest revision, all discussions resolved.

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Comments from Reviewable