Fix 2D Gizmos not always drawn on top (#17085)

# Objective

- As stated in the linked issue, if a Mesh2D is drawn with elements with
a positive Z value, resulting gizmos get drawn behind instead of in
front of them.
- Fixes #17053

## Solution

- Similar to the change done for the `SpritePipeline` in the relevant
commit (5abc32ceda), this PR changes both
line gizmos to avoid writing to the depth buffer and always pass the
depth test to ensure they are not filtered out.

## Testing

- Tested with the provided snippet in #17053 
- I looked over the `2d_gizmos` example, but it seemed like adding more
elements there to demonstrate this might not be the best idea? Looking
for guidance here on if that should be updated or if a new gizmo example
needs to be made.

crates/bevy_gizmos/src/pipeline_2d.rs

@@ -140,8 +140,8 @@ impl SpecializedRenderPipeline for LineGizmoPipeline {
             primitive: PrimitiveState::default(),
             depth_stencil: Some(DepthStencilState {
                 format: CORE_2D_DEPTH_FORMAT,
-                depth_write_enabled: true,
-                depth_compare: CompareFunction::GreaterEqual,
+                depth_write_enabled: false,
+                depth_compare: CompareFunction::Always,
                 stencil: StencilState {
                     front: StencilFaceState::IGNORE,
                     back: StencilFaceState::IGNORE,
@@ -241,8 +241,8 @@ impl SpecializedRenderPipeline for LineJointGizmoPipeline {
             primitive: PrimitiveState::default(),
             depth_stencil: Some(DepthStencilState {
                 format: CORE_2D_DEPTH_FORMAT,
-                depth_write_enabled: true,
-                depth_compare: CompareFunction::GreaterEqual,
+                depth_write_enabled: false,
+                depth_compare: CompareFunction::Always,
                 stencil: StencilState {
                     front: StencilFaceState::IGNORE,
                     back: StencilFaceState::IGNORE,