Harden allocators and mapper against Coverity safety paths

[akanisetti]

Issue types:

• Dereference null return value
• Explicit null dereferenced
• Overflowed constant
• Unchecked return value
• Use after free, Out-of-bounds access

Changes:

• Added null checks for gralloc handles and array append allocations
• Added input count validation in AIDL/HIDL allocator entry points
• Hardened PlaneLayouts buffer handling and driver null checks
• Replaced hidl_vec initializer-list construction with explicit resize/index assignment
• Added return-value checks for drmIoctl GEM_CLOSE and lseek SEEK_SET
• Guarded cross-domain metadata plane indexing against underflow
• Cleared drv->priv across virtgpu backend init/cleanup to prevent UAF

Tracked-On: NIACP3-1398