Add typescript build

[cmdcolin]

Possible method to upgrade @gmod/vcf to use typescript

Adds a "variant class" that keeps a handle to the parser object. Adds a toJSON method that should be used instead of spreading the variant object directly (which is done in VcfFeature) because that spreads the parser contents also. Could try to workaround this if this is undesirable, but there is a small change to the jbrowse 2 codebase for the VcfFeature->toJSON method.

[garrettjstevens]

I think that change is probably fine with a major version bump.

[cmdcolin]

This PR actually now has exact snapshot matches to the current main branch which is nice, uses private fields on the variant class to accomplish this

this has a minimum build ES2015 (unable to compile down to es5)

also the documentation module did not understand the private fields

produced error

yarn build
yarn run v1.22.15
$ npm run docs && npm run clean && npm run lint

> @gmod/vcf@5.0.2 docs
> documentation readme src/parse.ts --section API --parse-extension ts

SyntaxError: Unexpected token, expected ";" (13:9)
    at _class.raise (/home/cdiesh/src/gmod/vcf-js/node_modules/documentation/node_modules/@babel/parser/lib/index.js:3939:15)
    at _class.unexpected (/home/cdiesh/src/gmod/vcf-js/node_modules/documentation/node_modules/@babel/parser/lib/index.js:5248:16)
    at _class.semicolon (/home/cdiesh/src/gmod/vcf-js/node_modules/documentation/node_modules/@babel/parser/lib/index.js:5232:40)
    at _class.parseClassPrivateProperty (/home/cdiesh/src/gmod/vcf-js/node_modules/documentation/node_modules/@babel/parser/lib/index.js:8106:10)
    at _class.pushClassPrivateProperty (/home/cdiesh/src/gmod/vcf-js/node_modules/documentation/node_modules/@babel/parser/lib/index.js:8083:30)
    at _class.parseClassMemberWithIsStatic (/home/cdiesh/src/gmod/vcf-js/node_modules/documentation/node_modules/@babel/parser/lib/index.js:8009:14)
    at _class.parseClassMemberWithIsStatic (/home/cdiesh/src/gmod/vcf-js/node_modules/documentation/node_modules/@babel/parser/lib/index.js:10001:58)
    at _class.parseClassMember (/home/cdiesh/src/gmod/vcf-js/node_modules/documentation/node_modules/@babel/parser/lib/index.js:7948:10)
    at _class.parseClassMember (/home/cdiesh/src/gmod/vcf-js/node_modules/documentation/node_modules/@babel/parser/lib/index.js:9958:46)
    at _class.parseClassBody (/home/cdiesh/src/gmod/vcf-js/node_modules/documentation/node_modules/@babel/parser/lib/index.js:7903:12) {
  pos: 266,
  loc: Position { line: 13, column: 9 }
}

The line
loc: Position { line: 13, column: 9 }

Is exactly the line in src/parse.ts that the private field is used

So, documentation module removed for now

[garrettjstevens]

Looks good! Glad to see this get TypeScript-ified.

I was able to get documentation-js working, see here: add_tsc...add_tsc_gs, along with just a couple minor things to help avoid ts-ignores.

[cmdcolin]

excellent :)

[cmdcolin]

merged this branch here

[cmdcolin]

I was trying to use this branch under node.js and it was sufficiently difficult (since neither es2015 or es2018 are commonjs formats) and using ESM under nodejs is somewhat difficult to use (because it REQUIRES you to have extensions on your imports e.g. import THING from './filenameMustHaveExtension.js' see nodejs/node#30927) so keeping it an es5 option may improve usability, and it is not possible to have that if using the private fields

Therefore I made this branch go back to the dynamically created class type that is on the current master branch for this repo 3e31a3b