[clang-doc] Bump BitcodeWriter max line number to 32U

[juliehockett]

Summary

b43039 reports hitting the assert on a very large file, so bumping this to allow for larger files.

[phosek]

LGTM (small nit, people usually use PRXXX rather than bXXX to refer to issues)

clang-tools-extra/clang-doc/BitcodeWriter.h

 struct BitCodeConstants {
   static constexpr unsigned RecordSize = 32U;
   static constexpr unsigned SignatureBitSize = 8U;
   static constexpr unsigned SubblockIDSize = 4U;
   static constexpr unsigned BoolSize = 1U;
   static constexpr unsigned IntSize = 16U;
   static constexpr unsigned StringLengthSize = 16U;
   static constexpr unsigned FilenameLengthSize = 16U;
-  static constexpr unsigned LineNumberSize = 16U;
+  static constexpr unsigned LineNumberSize = 32U;
   static constexpr unsigned ReferenceTypeSize = 8U;
   static constexpr unsigned USRLengthSize = 6U;
   static constexpr unsigned USRBitLengthSize = 8U;
   static constexpr unsigned char Signature[4] = {'D', 'O', 'C', 'S'};
   static constexpr int USRHashSize = 20;
 };
 
 // New Ids need to be added to both the enum here and the relevant IdNameMap in