[ADF-3643] Viewer shows both sidebar icons

[eromano]

Please check if the PR fulfills these requirements

• The commit message follows our guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

What kind of change does this PR introduce? (check one with "x")

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation
• Other... Please describe:

What is the current behaviour? (You can also link to an open issue here)
Enable only right sidebar
Open the viewer

Current behaviour:
It shows two sidebar buttons, the left sidebar is empty.

Expected behavior:
It should be possible to switch off the left sidebar

Does this PR introduce a breaking change? (check one with "x")

• Yes
• No

If this PR contains a breaking change, please describe the impact and migration path for existing applications: ...

Other information:
https://issues.alfresco.com/jira/browse/ADF-3643

[codecov-io]

Codecov Report

Merging #3852 into development will increase coverage by 14.57%.
The diff coverage is 100%.

@@               Coverage Diff                @@
##           development    #3852       +/-   ##
================================================
+ Coverage         69.4%   83.97%   +14.57%     
================================================
  Files              760      765        +5     
  Lines            19900    19943       +43     
  Branches          2726     2727        +1     
================================================
+ Hits             13812    16748     +2936     
+ Misses            5426     2373     -3053     
- Partials           662      822      +160

Impacted Files	Coverage Δ
lib/core/viewer/components/viewer.component.ts	63.06% <100%> (+36.85%)	⬆️
...ices/task-list/components/attach-form.component.ts	60.71% <0%> (-5.36%)	⬇️
...e/login/components/login-dialog-panel.component.ts	91.66% <0%> (ø)	⬆️
lib/core/testing/core.testing.module.ts	100% <0%> (ø)
lib/core/mock/comment-content-service.mock.ts	100% <0%> (ø)
...b/core/form/components/widgets/core/group.model.ts	100% <0%> (ø)
lib/core/form/models/widget-visibility.model.ts	100% <0%> (ø)
lib/core/test.ts	100% <0%> (ø)
lib/core/utils/momentDateAdapter.ts	50% <0%> (+0.92%)	⬆️
...es/content-node-share/content-node-share.dialog.ts	83.14% <0%> (+1.21%)	⬆️
... and 165 more

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