[clang][ExtractAPI][NFC] Remove some nullptr dereference problems (#98914)

[daniel-grumberg]

A places try to get a NamedDecl's name using getName when it isn't a simple identifier, migrate these areas to getNameAsString.

rdar://125315602

[daniel-grumberg]

@swift-ci please test

[drodriguez]

I think this change introduces a failure in Clang :: ExtractAPI/enum.c test.

FAIL: Clang :: ExtractAPI/enum.c (16 of 57)
******************** TEST 'Clang :: ExtractAPI/enum.c' FAILED ********************
Script:
--
: 'RUN: at line 1';   rm -rf /Users/danielrodriguez/code/swift-source/build/my_macos/llvm-macosx-arm64/tools/clang/test/ExtractAPI/Output/enum.c.tmp
: 'RUN: at line 2';   split-file /Users/danielrodriguez/code/swift-source/llvm-project/clang/test/ExtractAPI/enum.c /Users/danielrodriguez/code/swift-source/build/my_macos/llvm-macosx-arm64/tools/clang/test/ExtractAPI/Output/enum.c.tmp
: 'RUN: at line 3';   sed -e "s@INPUT_DIR@/Users/danielrodriguez/code/swift-source/build/my_macos/llvm-macosx-arm64/tools/clang/test/ExtractAPI/Output/enum.c.tmp@g"  /Users/danielrodriguez/code/swift-source/build/my_macos/llvm-macosx-arm64/tools/clang/test/ExtractAPI/Output/enum.c.tmp/reference.output.json.in >> /Users/danielrodriguez/code/swift-source/build/my_macos/llvm-macosx-arm64/tools/clang/test/ExtractAPI/Output/enum.c.tmp/reference.output.json
: 'RUN: at line 5';   /Users/danielrodriguez/code/swift-source/build/my_macos/llvm-macosx-arm64/bin/clang -cc1 -internal-isystem /Users/danielrodriguez/code/swift-source/build/my_macos/llvm-macosx-arm64/lib/clang/17/include -nostdsysteminc -extract-api --pretty-sgf -triple arm64-apple-macosx    -x c-header /Users/danielrodriguez/code/swift-source/build/my_macos/llvm-macosx-arm64/tools/clang/test/ExtractAPI/Output/enum.c.tmp/input.h -o /Users/danielrodriguez/code/swift-source/build/my_macos/llvm-macosx-arm64/tools/clang/test/ExtractAPI/Output/enum.c.tmp/output.json -verify
: 'RUN: at line 9';   sed -e "s@\"generator\": \".*\"@\"generator\": \"?\"@g"  /Users/danielrodriguez/code/swift-source/build/my_macos/llvm-macosx-arm64/tools/clang/test/ExtractAPI/Output/enum.c.tmp/output.json >> /Users/danielrodriguez/code/swift-source/build/my_macos/llvm-macosx-arm64/tools/clang/test/ExtractAPI/Output/enum.c.tmp/output-normalized.json
: 'RUN: at line 11';   diff /Users/danielrodriguez/code/swift-source/build/my_macos/llvm-macosx-arm64/tools/clang/test/ExtractAPI/Output/enum.c.tmp/reference.output.json /Users/danielrodriguez/code/swift-source/build/my_macos/llvm-macosx-arm64/tools/clang/test/ExtractAPI/Output/enum.c.tmp/output-normalized.json
--
Exit Code: 1

Command Output (stdout):
--
681a682,687
>           }
>         ],
>         "subHeading": [
>           {
>             "kind": "identifier",
>             "spelling": ""
775a782,787
>         "subHeading": [
>           {
>             "kind": "identifier",
>             "spelling": ""
>           }
>         ],

--

********************
********************
Failed Tests (1):
  Clang :: ExtractAPI/enum.c

The JSON around the empty subheading seems to indicate that it comes from the anonymous enums towards the end of the input header.

Since this is a cherry-pick from LLVM upstream, I went looking for something different there, and I think some work done around ExtractAPI might be missing in this repository for the test to pass. At first I thought about llvm#87772 which is part of upstream, but I don't see in swift/release/6.0. It does not cherry-pick cleanly, but after solving a conflict, it doesn't seem to solve the test. I also tried llvm#93559, first by itself, which has several conflicts and did not compile, and then on top of the previous PR. That combination seems to remove the test failure.

Can we get those two cherry-picked into this branch so the test is passing? Thanks!