Can't handle bitflags bits method calls correctly

bitflags! {
    #[repr(transparent)]
    #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
    pub struct MemoryProtection: u32 {
        const NONE = 0;
        /// Execute
        const X = 1 << 0;
        /// Read
        const R = 1 << 1;
        /// Write
        const W = 1 << 2;
        /// Copy
        const C = 1 << 3;
        /// Execute and Read
        const XR = Self::X.bits() | Self::R.bits();
        /// Execute, Read and Write
        const XRW = Self::X.bits() | Self::R.bits() | Self::W.bits();
        /// Execute, Write and Copy
        const XWC = Self::X.bits() | Self::W.bits() | Self::C.bits();
        /// Read and Write
        const RW = Self::R.bits() | Self::W.bits();
        /// Write and Copy
        const WC = Self::W.bits() | Self::C.bits();
        /// Read and Copy
        const RC = Self::R.bits() | Self::C.bits();
        /// Read, Write and Copy
        const RWC = Self::R.bits() | Self::W.bits() | Self::C.bits();
    }
}

Generates:

using MemoryProtection = uint32_t;
constexpr static const MemoryProtection MemoryProtection_NONE = (uint32_t)0;
/// Execute
constexpr static const MemoryProtection MemoryProtection_X = (uint32_t)(1 << 0);
/// Read
constexpr static const MemoryProtection MemoryProtection_R = (uint32_t)(1 << 1);
/// Write
constexpr static const MemoryProtection MemoryProtection_W = (uint32_t)(1 << 2);
/// Copy
constexpr static const MemoryProtection MemoryProtection_C = (uint32_t)(1 << 3);
/// Execute and Read
constexpr static const MemoryProtection MemoryProtection_XR = (uint32_t)((MemoryProtection_X).bits | (MemoryProtection_R).bits);
/// Execute, Read and Write
constexpr static const MemoryProtection MemoryProtection_XRW = (uint32_t)(((MemoryProtection_X).bits | (MemoryProtection_R).bits) | (MemoryProtection_W).bits);
/// Execute, Write and Copy
constexpr static const MemoryProtection MemoryProtection_XWC = (uint32_t)(((MemoryProtection_X).bits | (MemoryProtection_W).bits) | (MemoryProtection_C).bits);
/// Read and Write
constexpr static const MemoryProtection MemoryProtection_RW = (uint32_t)((MemoryProtection_R).bits | (MemoryProtection_W).bits);
/// Write and Copy
constexpr static const MemoryProtection MemoryProtection_WC = (uint32_t)((MemoryProtection_W).bits | (MemoryProtection_C).bits);
/// Read and Copy
constexpr static const MemoryProtection MemoryProtection_RC = (uint32_t)((MemoryProtection_R).bits | (MemoryProtection_C).bits);
/// Read, Write and Copy
constexpr static const MemoryProtection MemoryProtection_RWC = (uint32_t)(((MemoryProtection_R).bits | (MemoryProtection_W).bits) | (MemoryProtection_C).bits);

The Problem:
Prints .bits

mostly related to #881

Start with the bitflags example and trace how cbindgen translates method calls such as .bits() in generated constants. Compare the behavior with the related work in #881, then add regression coverage showing that bitflag method calls are emitted as valid constant expressions without the unwanted .bits text.