[clang-format] Don't break lines after pragma region

We have autogenerated pragma regions in our code
which where awkwardly broken up like this:

```
#pragma region foo(bar : hello)
```
becomes

```
#pragma region foo(bar \
                   : hello)
```

This fixes the problem by adding region as a keyword
and handling it the same way as pragma mark

Reviewed By: curdeius

Differential Revision: https://reviews.llvm.org/D125961

clang/lib/Format/FormatToken.h

@@ -930,6 +930,7 @@ struct AdditionalKeywords {
     kw___has_include_next = &IdentTable.get("__has_include_next");
 
     kw_mark = &IdentTable.get("mark");
+    kw_region = &IdentTable.get("region");
 
     kw_extend = &IdentTable.get("extend");
     kw_option = &IdentTable.get("option");
@@ -1053,6 +1054,7 @@ struct AdditionalKeywords {
 
   // Pragma keywords.
   IdentifierInfo *kw_mark;
+  IdentifierInfo *kw_region;
 
   // Proto keywords.
   IdentifierInfo *kw_extend;

clang/lib/Format/TokenAnnotator.cpp

@@ -1251,9 +1251,9 @@ class AnnotatingParser {
   void parsePragma() {
     next(); // Consume "pragma".
     if (CurrentToken &&
-        CurrentToken->isOneOf(Keywords.kw_mark, Keywords.kw_option)) {
+        CurrentToken->isOneOf(Keywords.kw_mark, Keywords.kw_option, Keywords.kw_region)) {
       bool IsMark = CurrentToken->is(Keywords.kw_mark);
-      next(); // Consume "mark".
+      next();
       next(); // Consume first token (so we fix leading whitespace).
       while (CurrentToken) {
         if (IsMark || CurrentToken->Previous->is(TT_BinaryOperator))

clang/unittests/Format/FormatTest.cpp

@@ -19597,6 +19597,13 @@ TEST_F(FormatTest, UnderstandPragmaOption) {
   EXPECT_EQ("#pragma option -C -A", format("#pragma    option   -C   -A"));
 }
 
+TEST_F(FormatTest, UnderstandPragmaRegion) {
+  auto Style = getLLVMStyleWithColumns(0);
+  verifyFormat("#pragma region TEST(FOO : BAR)", Style);
+
+  EXPECT_EQ("#pragma region TEST(FOO : BAR)", format("#pragma region TEST(FOO : BAR)", Style));
+}
+
 TEST_F(FormatTest, OptimizeBreakPenaltyVsExcess) {
   FormatStyle Style = getLLVMStyleWithColumns(20);