[YAML] fix output incorrect format for block scalar string (#132897)

After outputting block scalar string, the indent will be wrong.
This patch fixes Padding after block scalar string to ensure the correct
format of yaml.

The new added ut will fail in main.
```diff
@@ -3,4 +3,4 @@
     Just a block
     scalar doc
-scalar:          a
+  scalar:          a
 ...\n
```

Author: HerrCai0907

llvm/lib/Support/YAMLTraits.cpp

@@ -725,18 +725,18 @@ void Output::blockScalarString(StringRef &S) {
   if (!StateStack.empty())
     newLineCheck();
   output(" |");
-  outputNewLine();
 
   unsigned Indent = StateStack.empty() ? 1 : StateStack.size();
 
   auto Buffer = MemoryBuffer::getMemBuffer(S, "", false);
   for (line_iterator Lines(*Buffer, false); !Lines.is_at_end(); ++Lines) {
+    outputNewLine();
     for (unsigned I = 0; I < Indent; ++I) {
       output("  ");
     }
     output(*Lines);
-    outputNewLine();
   }
+  outputUpToEndOfLine("");
 }
 
 void Output::scalarTag(std::string &Tag) {

llvm/test/CodeGen/AArch64/GlobalISel/arm64-irtranslator.ll

@@ -431,7 +431,6 @@ end:
 
 ; CHECK-LABEL: name: unreachable
 ; CHECK: G_ADD
-; CHECK-NEXT: {{^$}}
 ; CHECK-NEXT: ...
 define void @unreachable(i32 %a) {
   %sum = add i32 %a, %a

llvm/test/CodeGen/Generic/MIRStripDebug/no-metadata-present.mir

@@ -3,7 +3,6 @@
 # CHECK: name: test
 # CHECK: body: |
 # CHECK-NEXT: bb.0:
-# CHECK-EMPTY:
 # CHECK-NEXT: ...
 
 ---

llvm/test/CodeGen/MIR/AArch64/empty-MF.mir

@@ -3,7 +3,6 @@
 # CHECK-NEXT: ---
 # CHECK-NEXT: name:            foo
 # CHECK: body:             |
-# CHECK-EMPTY:
 # CHECK-NEXT: ...
 ---
 name: foo

llvm/test/tools/obj2yaml/Minidump/basic.yaml

@@ -114,7 +114,6 @@ Streams:
 # CHECK-NEXT:     Text:             |
 # CHECK-NEXT:       400d9000-400db000 r-xp 00000000 b3:04 227        /system/bin/app_process
 # CHECK-NEXT:       400db000-400dc000 r--p 00001000 b3:04 227        /system/bin/app_process
-# CHECK-EMPTY:
 # CHECK-NEXT:   - Type:            ModuleList
 # CHECK-NEXT:     Modules:
 # CHECK-NEXT:       - Base of Image:   0x1020304050607

llvm/unittests/Support/YAMLIOTest.cpp

@@ -1298,7 +1298,7 @@ TEST(YAMLIO, TestScalarAfterBlockScalar) {
 - block_scalac:     |
     AA
     BB
-scalar:          a
+  scalar:          a
 ...
 )");
 }