TransformableInfo should support symbols as keys

[dancrumb]

Being able to use a Symbol as a key for TransformableInfo makes it easier to create cleaner transforms.

The current typing forbids this, so this change enables it.

[dscalzi]

cc @wbt please merge this, it has been a problem for over two years. It's incredibly annoying to have to copy the same typings patch on every project that uses winston.

This project looks largely unmaintained, but this is a zero-effort solution to a frustrating issue.

[dscalzi]

reference: #111 #114

[wbt]

cc @wbt please merge this, it has been a problem for over two years. It's incredibly annoying to have to copy the same typings patch on every project that uses winston.

FYI @dscalzi, that claim seems a bit less than truthful given that TS support for this is only about a year and a half old.

this is a zero-effort solution

Also not true, for me or according to the folks complaining at #244.

[dscalzi]

The issue was first reported more than 2 years ago and never received a response. Moreover, this package has provided a .d.ts file for 5 years https://github.com/winstonjs/logform/commits/master/index.d.ts, not only a year and a half.

[dscalzi]

See #15 ...

[wbt]

Support for using symbols as index types, which is what this specific PR is about, has only been released for a year and a half.
That is what's causing problems at #244 - it's too recent a feature in TS.