Create new disambiguator to remove warning when building docs

[jakovljevic-mladen]

Since operators are now exported from top level module (as of #6488), when building docs, a multiple warnings are produced. For example:

warn:    Error in {@link raceWith} - Ambiguous link: "raceWith".
Matching docs:
  "index/raceWith" (function) : (api/index/function/raceWith / internal/operators/raceWith.ts)
  "operators/raceWith" (function) : (api/operators/raceWith / internal/operators/raceWith.ts) - doc "api/deprecations" (deprecation)

The reason is that there are multiple documents that exist in two modules: index module and operators module. For this reason, {@link raceWith} won't work since package that builds links can't decide which one to take. Thus, a new disambiguator should be created to remove operators from operators module.