[clang-format] Unstable output with AllowShortFunctionsOnASingleLine=inline

[vient]

Somewhat minified test case:

void f() {
#define M(x)     \
  case 0: {      \
    return {#x}; \
  }
}

Formatting it with clang-format-18 -Werror --style='{AllowShortFunctionsOnASingleLine: Inline}' results in oscillating outputs - original code produces output 1, it produces output 2, which produces output 1, and so on (1️⃣🔄2️⃣).
Output 1:

void f() {
#define M(x)                                                                   \
  case 0: {                                                                    \
    return {                                                                   \
      #x                                                                       \
    };                                                                         \
  }
}

Output 2:

void f() {
#define M(x)                                                                   \
  case 0: {                                                                    \
    return {#x};                                                               \
  }
}

It is a regression in clang-format-18, 17 works fine. Issue is still present in clang-format-19, did not check with trunk.

[vient]

This test does not produce oscillating behavior but still takes two runs to converge

void f() {
#define M(x)     \
    return {#x}; 
}

becomes

void f() {
#define M(x)                                                                   \
  return {                                                                     \
    #x                                                                         \
  };
}

which then becomes

void f() {
#define M(x) return {#x};
}

Macro parameter (x) can be removed but {#x} part seems to be crucial - removing # makes the issue go away in both this and original test.