intel/brw: Use fs_visitor instead of backend_shader in various passes

And since we are touching them, rename a couple of passes
to follow same name convention as existing ones.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/27861>

src/intel/compiler/brw_schedule_instructions.cpp

@@ -586,7 +586,7 @@ schedule_node::set_latency(const struct brw_isa_info *isa)
 
 class instruction_scheduler {
 public:
-   instruction_scheduler(void *mem_ctx, const backend_shader *s, int grf_count,
+   instruction_scheduler(void *mem_ctx, const fs_visitor *s, int grf_count,
                          int grf_write_scale, bool post_reg_alloc):
       bs(s)
    {
@@ -662,7 +662,7 @@ public:
 
    bool post_reg_alloc;
    int grf_count;
-   const backend_shader *bs;
+   const fs_visitor *bs;
 
    /**
     * Last instruction to have written the grf (or a channel in the grf, for the