[MatMul] Update generated code after memory index hoisting

[shmsong]

All changes in this PR are minor tweaking on the generated cuda code to get the intended assembly code after compilation.

Here is a list of minor codegen tweaking grouped into this PR: (more details see comments and internal doc)

---

1.Double Buffer Swtich to ensure UR usage in double buffered indexing

Before transform:

for i in ... // double buffer loop:
  .. = ld.shared [... + i%3 *double_buffer_size]

After transform:

double_buffer_switch=0;
for i in ... // double buffer loop:
  .. = ld.shared [... + double_buffer_switch]
  double_buffer_switch = update(double_buffer_switch, double_buffer_size);

---

2. Double Buffer Update to save register when UR is not available, this costs more instructions.

Before transform:

for i in ... // double buffer loop:
  .. = ld.shared [... + i%3 *double_buffer_size]

After transform:

for j in ...
  R[j] = ...
for i in ... // double buffer loop:
  .. = ld.shared [R[J]]
  for j in ...
     R[j]= update(R[j], double_buffer_size);

---

3.Casting lifted component to byte pointer: lifts some instructions and regs out of main loop

Before transform:

nvfuser_index_t base = ...
for i in ... // main loop
  .. = ld.global &T0[base+123]

After transform:

char* base = &T0[[...]
for i in ... // main loop
  .. = ld.global base+123*sizeof(T0.dtype)

---

4.Increment gmem pointer: lifts some more instructions and regs out of main loop

Before transform:

char* base = ...
for i in ... // main loop
  .. = ld.global base+123* i

After transform:

char* base = ...
for i in ... // main loop
  .. = ld.global base
  base+=123

---

5.Decrement gmem pointer: improves the instruction schedule
Before transform:

char* base = ...
for i in ... // main loop
  .. = ld.global base
  base+=123

After transform:

char* base = ...
base -=123
for i in ... // main loop
  base+=123
  .. = ld.global base

---

6. lift cvta out of main loop for cp.async: ensures usage of immediate field.
   Before transform:

char* smem_ptr = ...
for i in ... // main loop
 cp.async smem_ptr+123, ...

After transform:

char* smem_ptr = ...
unsigned smem_address = cvta(smem_ptr);
for i in ... // main loop
 cp.async smem_address +123, ...

[naoyam]

@shmsong Just skimmed through the changes. As far as I cans see, there's nothing fundamentally new analysis in this PR, but all of the changes are more like localized tweaking of generated codes as you explained in the above comment. In the interest of the time, I'll prioritize the other PRs to review.