clang-format: Allow optimizer to break template declaration.

Summary:
Introduce `PenaltyBreakTemplateDeclaration` to control the penalty,
and change `AlwaysBreakTemplateDeclarations` to an enum with 3 modes:
* `No` for regular, penalty based, wrapping of template declaration
* `MultiLine` for always wrapping before multi-line declarations (e.g.
  same as legacy behavior when `AlwaysBreakTemplateDeclarations=false`)
* `Yes` for always wrapping (e.g. same as legacy behavior when
  `AlwaysBreakTemplateDeclarations=true`)

Reviewers: krasimir, djasper, klimek

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D42684

llvm-svn: 332436