Migrating to Typescript

[seiyab]

What this PR changes?

• Migrates Flow -> TypeScript
• Migrates standard -> ts-standard (Official variant for TypeScript)
• Adds lint and type check for ui into build setting
• Resolves (or sometimes ignores) type errors.

What I'm planning after this PR

• Opening issue about any or ts-ignore so that digdag-ui will become more reliable
• Opening issue about eslint-disable so that digdag-ui will become more relieable
• Submitting PRs that resolve some parts of issues above

For reviewers, and for contributors who will come here from commit history

• I didn't resolve many typing / lint problems so that I can work this PR feasibly
  • So any, ts-ignore and eslint-disable are not desired ones. Resolving them should be welcome

[seiyab]

@szyn Could you review this? It is likely to conflict every digdag-ui change.

[seiyab]

I found that current master fails on type check (./gradlew digdag-ui:checkUi)

console.tsx(2041,34): error TS2769: No overload matches this call.
  Overload 1 of 2, '(data: Data, options: InflateFunctionOptions & { to: "string"; }): string', gave the following error.
    Argument of type 'Data | null' is not assignable to parameter of type 'Data'.
      Type 'null' is not assignable to type 'Data'. 
  Overload 2 of 2, '(data: Data, options?: InflateFunctionOptions | undefined): Uint8Array', gave the following error.
    Argument of type 'Data | null' is not assignable to parameter of type 'Data'.

> Task :digdag-ui:checkUi FAILED

@szyn @yoyama Should I add ./gradlew digdag-ui:checkUi or npm run type into GitHub actions? I'm confused by another error in ./gradlew check. I've supposed that ./gradlew check should run on CI.

> Task :digdag-standards:test                                                                                                                                                                               

io.digdag.standards.operator.td.TdBaseTdJobOperatorTest > initializationError FAILED                                                                                                                        
    org.objenesis.ObjenesisException at SunReflectionFactoryHelper.java:54                                                                                                                                  
        Caused by: java.lang.reflect.InvocationTargetException at NativeMethodAccessorImpl.java:-2
            Caused by: java.lang.IllegalAccessError at ClassLoader.java:-2
WARNING: An illegal reflective access operation has occurred
WARNING: Illegal reflective access by org.eclipse.jetty.util.BufferUtil (file:~/.gradle/caches/modules-2/files-2.1/org.eclipse.jetty/jetty-util/9.3.11.v20160721/1812ffd5a04698051180d582c146ca80
7760c808/jetty-util-9.3.11.v20160721.jar) to field java.nio.MappedByteBuffer.fd
WARNING: Please consider reporting this to the maintainers of org.eclipse.jetty.util.BufferUtil
WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
WARNING: All illegal access operations will be denied in a future release

304 tests completed, 1 failed                       

> Task :digdag-standards:test FAILED