build: upgrade typescript to 3.8.2

[ktmud]

CATEGORY

Choose one

• Bug Fix
• Enhancement (new features, refinement)
• Refactor
• Add tests
• Build / Development Environment
• Documentation

SUMMARY

Some @superset-ui-plugin uses newer version of Typescript and the build may fail when you try to import the Typescript directly via npm link.

• Upgrade Typescript to 3.8.2 and fix minor linting issues.
• Change webpack stats to "minimal" so build errors are more readable.
• Move .gitignore for frontend code to its own subfolder.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

TEST PLAN

All CI/CD should pass.

ADDITIONAL INFORMATION

• Has associated issue:
• Changes UI
• Requires DB Migration.
• Confirm DB Migration upgrade and downgrade tested.
• Introduces new feature or API
• Removes existing feature or API

REVIEWERS

[codecov-io]

Codecov Report

Merging #9189 into master will decrease coverage by 0.19%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           master    #9189     +/-   ##
=========================================
- Coverage   59.13%   58.93%   -0.2%     
=========================================
  Files         372      372             
  Lines       11938    11987     +49     
  Branches     2925     2936     +11     
=========================================
+ Hits         7059     7065      +6     
- Misses       4699     4742     +43     
  Partials      180      180

Impacted Files	Coverage Δ
...uperset-frontend/src/views/chartList/ChartList.tsx	63.39% <0%> (-11.1%)	⬇️
...frontend/src/views/dashboardList/DashboardList.tsx	59.34% <0%> (-10.38%)	⬇️
...rset-frontend/src/components/ListView/ListView.tsx	86.02% <0%> (-6.39%)	⬇️
superset-frontend/src/components/ListView/utils.ts	94.44% <0%> (-4.02%)	⬇️
superset-frontend/src/components/Menu/Menu.jsx	87.5% <0%> (ø)	⬆️

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[etr2460]

a few comments, thanks for the upgrade!