[clang-tidy] readability-simplify-boolean-expr should handle if statements with init statements

[denzor200]

Problem: readability-simplify-boolean-expr doesn't simplify conditions in if statements with init statements.

Examples:

• if (auto x = f(); x != nullptr) → if (auto x = f())
• if (bool b = g(); b == true) → if (bool b = g())

Request: Extend the check to handle C++17 if-with-initializer syntax.

[llvmbot]

@llvm/issue-subscribers-clang-tidy

Author: Denis Mikhailov (denzor200)

**Problem:** `readability-simplify-boolean-expr` doesn't simplify conditions in if statements with init statements.

Examples:

• if (auto x = f(); x != nullptr) → if (auto x = f())
• if (bool b = g(); b == true) → if (bool b = g())

Request: Extend the check to handle C++17 if-with-initializer syntax.