SymbolVendor: Make SectionAddressesChanged a passthrough

Summary:
This moves the implementation of the function into the SymbolFile class,
making it possible to excise the SymbolVendor passthrough functions in
follow-up patches.

Reviewers: clayborg, jingham, JDevlieghere

Subscribers: lldb-commits

Differential Revision: https://reviews.llvm.org/D65266

llvm-svn: 367231