`FormatMoney(CAmount n)` is not being properly defined for `n = std::numeric_limits<CAmount>::min()`. This is due to an invalid integer negation: the negation of `-9223372036854775808` cannot be represented in type `CAmount` (which has a max value of `9223372036854775807`):

https://github.com/bitcoin/bitcoin/blob/54f812d9d29893c690ae06b84aaeab128186aa36/src/util/moneystr.cpp#L12-L31

FWIW `FormatMoney(-9223372036854775808)` returns `--92233720368.-54775808` when compiled with UBSan (LLVM/Clang, `-fsanitize=undefined`).

Context: https://github.com/bitcoin/bitcoin/pull/20383#discussion_r523250890

It would be nice if `FormatMoney(CAmount n)` was properly defined for all `CAmount n` :)

These are the "expectations of least surprise":

```
BOOST_CHECK_EQUAL(FormatMoney(std::numeric_limits<CAmount>::max()), "92233720368.54775807");       //  9223372036854775807
BOOST_CHECK_EQUAL(FormatMoney(std::numeric_limits<CAmount>::max() - 1), "92233720368.54775806");   //  9223372036854775806
BOOST_CHECK_EQUAL(FormatMoney(std::numeric_limits<CAmount>::max() - 2), "92233720368.54775805");   //  9223372036854775805
BOOST_CHECK_EQUAL(FormatMoney(std::numeric_limits<CAmount>::max() - 3), "92233720368.54775804");   //  9223372036854775804
BOOST_CHECK_EQUAL(FormatMoney(std::numeric_limits<CAmount>::min() + 3), "-92233720368.54775805");  // -9223372036854775805
BOOST_CHECK_EQUAL(FormatMoney(std::numeric_limits<CAmount>::min() + 2), "-92233720368.54775806");  // -9223372036854775806
BOOST_CHECK_EQUAL(FormatMoney(std::numeric_limits<CAmount>::min() + 1), "-92233720368.54775807");  // -9223372036854775807
BOOST_CHECK_EQUAL(FormatMoney(std::numeric_limits<CAmount>::min()), "-92233720368.54775808");      // -9223372036854775808
```

These assertions are _guaranteed_ to hold for all cases above _except_ for the last one.
uint256 deserialized_u256;
        stream << u256;
        stream >> deserialized_u256;
        assert(u256 == deserialized_u256 && stream.empty());
        uint160 deserialized_u160;
        stream << u160;
        stream >> deserialized_u160;
        assert(u160 == deserialized_u160 && stream.empty());
        uint64_t deserialized_u64;
        stream << u64;
        stream >> deserialized_u64;
        assert(u64 == deserialized_u64 && stream.empty());
        int64_t deserialized_i64;
        stream << i64;
        stream >> deserialized_i64;
        assert(i64 == deserialized_i64 && stream.empty());
        uint32_t deserialized_u32;
        stream << u32;
        stream >> deserialized_u32;
        assert(u32 == deserialized_u32 && stream.empty());
        int32_t deserialized_i32;
        stream << i32;
        stream >> deserialized_i32;
        assert(i32 == deserialized_i32 && stream.empty());
        uint16_t deserialized_u16;
        stream << u16;
        stream >> deserialized_u16;
        assert(u16 == deserialized_u16 && stream.empty());
        int16_t deserialized_i16;
        stream << i16;