[clang-tools-extra] [clang-tidy] Add modernize-use-to-underlying check (PR #210459)

[Yanzuo Liu via cfe-commits]

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@@ -0,0 +1,55 @@
+// RUN: %check_clang_tidy -check-suffixes=IGNORE -std=c++23-or-later %s \
+// RUN:   modernize-use-to-underlying %t -- \
+// RUN:   -config="{CheckOptions: {modernize-use-to-underlying.ImpreciseCasts: Ignore}}"
+// RUN: %check_clang_tidy -check-suffixes=WARN -std=c++23-or-later %s \
+// RUN:   modernize-use-to-underlying %t -- \
+// RUN:   -config="{CheckOptions: {modernize-use-to-underlying.ImpreciseCasts: Warn}}"
+// RUN: %check_clang_tidy -check-suffixes=PRESERVE -std=c++23-or-later %s \
+// RUN:   modernize-use-to-underlying %t -- \
+// RUN:   -config="{CheckOptions: {modernize-use-to-underlying.ImpreciseCasts: PreserveType}}"
----------------
zwuis wrote:

```suggestion
// RUN: %check_clang_tidy -check-suffixes=COMMON -std=c++23-or-later %s \
// RUN:   modernize-use-to-underlying %t -- \
// RUN:   -config="{CheckOptions: {modernize-use-to-underlying.ImpreciseCasts: Ignore}}"
// RUN: %check_clang_tidy -check-suffixes=COMMON -std=c++23-or-later %s \
// RUN:   modernize-use-to-underlying %t -- \
// RUN:   -config="{CheckOptions: {modernize-use-to-underlying.ImpreciseCasts: Warn}}"
// RUN: %check_clang_tidy -check-suffixes=COMMON,PRESERVE -std=c++23-or-later %s \
// RUN:   modernize-use-to-underlying %t -- \
// RUN:   -config="{CheckOptions: {modernize-use-to-underlying.ImpreciseCasts: PreserveType}}"
```

To simplify `// CHECK`s.

https://github.com/llvm/llvm-project/pull/210459