Added a new --omit-names (-O, uppercase letter o) option to "type summary add".

When used in conjunction with --inline-children, this option will cause the names of the values to be omitted from the output. This can be beneficial in cases such as vFloat, where it will compact the representation from
([0]=1,[1]=2,[2]=3,[3]=4) to (1, 2, 3, 4).
Added a test case to check that the new option works correctly.
Also took some time to revisit SummaryFormat and related classes and tweak them for added readability and maintainability.
Finally, added a new class name to which the std::string summary should be applied.

llvm-svn: 149644