add options to disable mangling variable names of some functions

[HolgerJeromin]

feature request
My code has a big section of private code, but also a public API. Both are full of jsdoc annotations.

The API part has @preserve annotation (very nice feature!), so my users have jsdoc for intellisense support. It would be nice if we could skip mangling variable names for those API functions, so provide better support in chrome devTools console in runtime:

Without mangling we have

ref #3263

[alexlamsl]

Use mangle.reserved

[HolgerJeromin]

I had to add about 100 variable names in the array, but it worked.
This approach is not so easy to maintain and has the drawback to not mangle private code.
Thanks for the hint!