[clang-format][NFC] Extract some alignment tests

FormatTest.cpp is too huge, extract some tests to mitigate this a bit.

clang/unittests/Format/CMakeLists.txt

@@ -2,6 +2,7 @@
 # distinct target enables faster iteration times at low cost.
 add_distinct_clang_unittest(FormatTests
   AlignBracketsTest.cpp
+  AlignmentTest.cpp
   BracesInserterTest.cpp
   BracesRemoverTest.cpp
   CleanupTest.cpp