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This change adds support for typescript transpilation to our frontend
build via babel, and also updates eslint and canvas_i18nliner to be
able to understand typescript as well. The main goal of this PS is to
enable developers to add typescript code to the Canvas codebase but to
be unopinionated about how type-checking is done; at this stage types
will only be checked by running the new `check:ts` or `check:js`
scripts (which run the typescript compiler directly), or via
integration with an IDE like RubyMine or VS Code.

closes LS-2430
flag = none

Test plan:
  BUILD STEPS:
  - FE build, i18n build, and tests pass Jenkins
  - `bin/rails canvas:compile_assets` still works
  - `RAILS_ENV=production bin/rails convas:compile_assets` still works

  SPOT CHECKING:
  - Starting up rails and run `yarn build:js:watch`
  - Click around Canvas and make sure the frontend still loads as
    normal

Change-Id: I8bb1a0f065e09496a924708dead6fa4518b59496
Reviewed-on: https://gerrit.instructure.com/c/...