Strip enum member type name from sibling references in initializers

[tannergooding]

Fixes #576.

With strip-enum-member-type-name, member declarations were stripped but references to sibling members inside an initializer kept the enum type prefix, so the output referenced undefined names:

public enum WGPUInstanceBackend
{
    Vulkan = 1 << 0,
    Metal = 1 << 2,
    Primary = WGPUInstanceBackend_Vulkan | WGPUInstanceBackend_Metal,  // undefined
}

VisitDeclRefExpr computed the reference name with EscapeName and never applied the same stripping used when emitting the declaration (EscapeAndStripEnumMemberName in VisitEnumConstantDecl). Apply that transform to enum constant references, keyed off the referenced member's own enum type name, so references match their declarations:

    Primary = Vulkan | Metal,

EscapeAndStripEnumMemberName is a no-op when the option is off, so non-strip output is byte-identical (verified: no golden changed). Anonymous enums are left untouched, and cross-enum references still resolve via the existing using static path.

Added StripEnumMemberReferenceTest. Build 0 warning / 0 error; full suite green.

Note

This PR description and the code change were drafted by Copilot on my behalf.