feat: add support for unknown in typescript

[RichiCoder1]

Adds support for unknown (and it's flow equivalent) in TypeScript.

First PR and I made this constribution mostly via the GitHub UI, happy to do more if needed!

Closes #1619

[dvdsgl]

Awesome! Please add an option for this in the typescript test fixture.

[RichiCoder1]

@dvdsgl absolutely! Pulled down source to attempt this, but I'm not sure where in tests I'd add the specific options?

Also ran into this issue while executing npm run test:

[INFO] Compiling 3 source files to /workspaces/quicktype/test/fixtures/java/target/classes
[INFO] -------------------------------------------------------------
[ERROR] COMPILATION ERROR : 
[INFO] -------------------------------------------------------------
[ERROR] Source option 6 is no longer supported. Use 7 or later.
[ERROR] Target option 6 is no longer supported. Use 7 or later.
[INFO] 2 errors 
[INFO] -------------------------------------------------------------
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  4.015 s
[INFO] Finished at: 2023-03-01T20:56:22Z
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.10.1:compile (default-compile) on project QuickTypeTest: Compilation failure: Compilation failure: 
[ERROR] Source option 6 is no longer supported. Use 7 or later.
[ERROR] Target option 6 is no longer supported. Use 7 or later.
[ERROR] -> [Help 1]
[ERROR] 
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR] 
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoFailureException

[dvdsgl]

Check the README for details. You want quicktestRenderSettings or some such name.

[RichiCoder1]

https://github.com/quicktype/quicktype/blob/master/test/languages.ts#L694 it looks like?

[RichiCoder1]

Yup that was it. Actually found an unrelated bug, but icing this PR for a second. The source uses "any" as a catchall in a number of places where a more specific type (Record<key, unknown>, IConvertable) would make more sense which means a decent size chunk-o-changes will likely need to be made to the JavaScript output to emit the correct and specific types.

[SBrandeis]

@RichiCoder1 are there any plans to move forward with this PR?