[Docs] Use --stripInternal in TypeDoc

[deyaaeldeen]

#12912 removes the use of the @ignore JSDoc tag from our code base and replaces it with @internal. For the latter to work, we need to pass --stripInternal to TypeDoc.

IIRC, there are two documentation systems being used where this flag should be used

• https://azure.github.io/azure-sdk-for-js/
• https://docs.microsoft.com/en-us/javascript/api/overview/azure/?view=azure-node-latest

--stripInternal is introduced in TypeDoc v0.15.2.