[clang] [Clang] Bugfixes and improved support for `AttributedType`s in lambdas (PR #85325)

[LLVM Continuous Integration via cfe-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `llvm-clang-x86_64-sie-win` running on `sie-win-worker` while building `clang` at step 7 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/46/builds/5553

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 7 (test-build-unified-tree-check-all) failure: test (failure)
******************** TEST 'Clang :: SemaCXX/lambda-attributes.cpp' FAILED ********************
Exit Code: 1

Command Output (stdout):
--
# RUN: at line 1
z:\b\llvm-clang-x86_64-sie-win\build\bin\clang.exe -cc1 -internal-isystem Z:\b\llvm-clang-x86_64-sie-win\build\lib\clang\20\include -nostdsysteminc -std=c++23 -fsyntax-only -verify Z:\b\llvm-clang-x86_64-sie-win\llvm-project\clang\test\SemaCXX\lambda-attributes.cpp
# executed command: 'z:\b\llvm-clang-x86_64-sie-win\build\bin\clang.exe' -cc1 -internal-isystem 'Z:\b\llvm-clang-x86_64-sie-win\build\lib\clang\20\include' -nostdsysteminc -std=c++23 -fsyntax-only -verify 'Z:\b\llvm-clang-x86_64-sie-win\llvm-project\clang\test\SemaCXX\lambda-attributes.cpp'
# .---command stderr------------
# | error: 'expected-error' diagnostics seen but not expected: 
# |   File Z:\b\llvm-clang-x86_64-sie-win\llvm-project\clang\test\SemaCXX\lambda-attributes.cpp Line 18: 'preserve_most' calling convention is not supported for this target
# |   File Z:\b\llvm-clang-x86_64-sie-win\llvm-project\clang\test\SemaCXX\lambda-attributes.cpp Line 29: 'preserve_most' calling convention is not supported for this target
# |   File Z:\b\llvm-clang-x86_64-sie-win\llvm-project\clang\test\SemaCXX\lambda-attributes.cpp Line 40: 'preserve_most' calling convention is not supported for this target
# |   Line 45: 'preserve_most' calling convention is not supported for this target
# |   Line 48: 'preserve_most' calling convention is not supported for this target
# |   Line 53: 'preserve_most' calling convention is not supported for this target
# | 6 errors generated.
# `-----------------------------
# error: command failed with exit status: 1

--

********************


```

</details>

https://github.com/llvm/llvm-project/pull/85325