Shorten sanitizer plugin names

Summary:
The new UndefinedBehaviorSanitizer plugin was breaking file path length
limits, because it's (fairly long name) appears multiple times in the
path. Cmake ends up putting the object file at path
tools/lldb/source/Plugins/InstrumentationRuntime/UndefinedBehaviorSanitizer/CMakeFiles/lldbPluginInstrumentationRuntimeUndefinedBehaviorSanitizer.dir/UndefinedBehaviorSanitizerRuntime.cpp.obj
which is 191 characters long and very dangerously close to the 260
character path limit on windows systems (also, just the include line for
that file was breaking the 80 character line limit).

This renames the sanitizer plugins to use shorter names (asan, ubsan,
tsan). I think this will still be quite understandable to everyone as
those are the names everyone uses to refer to them anyway.

Reviewers: zturner, kubamracek, jingham

Subscribers: lldb-commits, mgorny

Differential Revision: https://reviews.llvm.org/D34553

llvm-svn: 306278