feat: Add fixed-size array support to the Go code generator

[statxc]

Summary

Add fixed-size array support to the Go code generator, resolving a long-standing gap where Go was the only major language without support for the [type:length] struct field syntax (fixes #8417).

Changes

• src/idl_parser.cpp: Add IDLOptions::kGo to the SupportsAdvancedArrayFeatures() allowlist.
• src/idl_gen_go.cpp: Implement array-aware code generation for Go, including:
  • Indexed accessors and length methods for scalar and struct array fields
  • Scalar array mutators with bounds-checked index access
  • Builder body logic with correct reverse-order writing and nested struct flattening
  • Object API (Pack/UnPack) support using Go fixed-size arrays ([N]Type)
• tests/go_arrays_test_test.go: Comprehensive test covering read, mutate, object API round-trip, and standalone struct creation against the arrays_test.fbs schema.
• tests/GoArraysTest.sh: Test runner script following the same pattern as GoTest.sh.

Design

The implementation follows the same flattening strategy used by the Java and C# generators: nested struct array fields are expanded into per-sub-field slices in the Create function signature. For example, d:[NestedStruct:2] becomes d_a [][]int32, d_b []TestEnum, d_c [][]TestEnum, d_d [][]int64. Field offsets were verified against the Java reference output.

Test plan

• go vet clean on generated code
• All 4 new tests pass (TestArrayStructRead, TestArrayStructMutate, TestArrayStructObjectAPI, TestNestedStructStandalone)
• Existing Go tests (GoTest.sh) still pass
• flatc builds with no warnings

[statxc]

@jtdavis777 would you review this PR
thank you

[jtdavis777]

this is also a language I am not familiar with, and that I think we do not have an active maintainer of. so will take me some time

[statxc]

Please any updates for me 🙏