[clang-format] Add support for absl nullability macros (#130346)

Add support for formatting w/ absl nullability macros
(https://github.com/abseil/abseil-cpp/blob/c52afac4f87ef76e6293b84874e5126a62be1f15/absl/base/nullability.h#L237).
Example at https://godbolt.org/z/PYv19M1Gj
input:
```
std::vector<int* _Nonnull> x;
std::vector<int* absl_nonnull> y;
```

orig output:
```
std::vector<int* _Nonnull> x;
std::vector<int * absl_nonnull> y;
```

new output:
```
std::vector<int* _Nonnull> x;
std::vector<int* absl_nonnull> y;
```
credit to @ymand for the original patch

1 files changed, 5 insertions, 0 deletions

diff --git a/clang/unittests/Format/ConfigParseTest.cpp b/clang/unittests/Format/ConfigParseTest.cpp
index 273bab8..cc42642 100644
--- a/clang/unittests/Format/ConfigParseTest.cpp
+++ b/clang/unittests/Format/ConfigParseTest.cpp
@@ -909,6 +909,11 @@ TEST(ConfigParseTest, ParsesConfiguration) {
   Style.AttributeMacros.clear();
   CHECK_PARSE("BasedOnStyle: LLVM", AttributeMacros,
               std::vector<std::string>{"__capability"});
+  CHECK_PARSE(
+      "BasedOnStyle: Google", AttributeMacros,
+      std::vector<std::string>({"__capability", "absl_nonnull", "absl_nullable",
+                                "absl_nullability_unknown"}));
+  Style.AttributeMacros.clear();
   CHECK_PARSE("AttributeMacros: [attr1, attr2]", AttributeMacros,
               std::vector<std::string>({"attr1", "attr2"}));