chore: export API singleton types

[dyladan]

This will fix the currently-failing lint workflow.

An update to typedoc means that only classes which are exported are included in the documentation. Here, the API singletons are exported as type only. This means they can't be used directly, but are included in the typedoc documentation and the following code will compile successfully:

import { context, ContextAPI } from "@opentelemetry/api";

let ctx: ContextAPI = context;

The following code will still fail:

import { ContextAPI } from "@opentelemetry/api";

const ctx = new ContextAPI() // this will fail
const ctx2 = ContextAPI.getInstance() // this will also fail

[codecov]

Codecov Report

Merging #1864 (2eeb611) into main (1eed360) will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #1864      +/-   ##
==========================================
- Coverage   92.37%   92.35%   -0.02%     
==========================================
  Files         157      157              
  Lines        5104     5104              
  Branches     1085     1085              
==========================================
- Hits         4715     4714       -1     
- Misses        389      390       +1     

Impacted Files	Coverage Δ
...emetry-core/src/platform/node/RandomIdGenerator.ts	87.50% <0.00%> (-6.25%)	⬇️

[dyladan]

@obecny ptal before merge because this affects API

[obecny]

lgtm