Report AD checkpoint contexts

[venkataram-nv]

Issue: #4997

Display checkpoint context structures for functions with non-empty contexts:

• Enabled with the flag -report-checkpoint-intermediates
• Report checkpoint context sides, including sizes of each field and where they were generated from
• Includes a lot of sourceLoc copies so that the source locations can be displayed

output for reverse-loop.slang

.\reverse-loop.slang(14): note: checkpointing context of 24 bytes associated with function: 'test_simple_loop'
float test_simple_loop(float y)
      ^~~~~~~~~~~~~~~~
.\reverse-loop.slang(17): note: 20 bytes (FixedArray<float, 5> ) used to checkpoint the following item:
    float t = y;
          ^
.\reverse-loop.slang(20): note: 4 bytes (int32_t) used for a loop counter here:
    for (int i = 0; i < 3; i++)
    ^~~

output for reverse-loop-checkpoint-test.slang

.\reverse-loop-checkpoint-test.slang(51): note: checkpointing context of 20 bytes associated with function: 'computeLoop'
float3 computeLoop(float y)
       ^~~~~~~~~~~
.\reverse-loop-checkpoint-test.slang(54): note: 4 bytes (float) used to checkpoint the following item:
    float w = 0;
          ^
.\reverse-loop-checkpoint-test.slang(57): note: 12 bytes (Vector<float, 3> ) used to checkpoint the following item:
    float3 w3 = float3(0, 0, 0);
           ^~
.\reverse-loop-checkpoint-test.slang(60): note: 4 bytes (int32_t) used for a loop counter here:
    for (int i = 0; i < 8; i++)
    ^~~

[saipraveenb25]

Overall, this looks good!

However, we really need tests for this. I would suggest that we use the diagnostic sink to report these diagnostics as 'notes' (use Severity::Note in the diagnostic info) and use file-check to write the tests.

[csyonghe]

We need to test for nested functions calls too.

If f calls g which has x byte of context, how is that reported?

[venkataram-nv]

@csyonghe The following is what it looks like for nested calls:

tests/autodiff/reverse-nested-calls.slang(19): note: checkpointing context of 4 bytes was generated for function: 'f'
float f(float x)
      ^
tests/autodiff/reverse-nested-calls.slang(21): note: 4 bytes (float) used to checkpoint the following item:
    return 3.0f * g(2.0f * x);
                   ^

[csyonghe]

Instead of setting source locs everywhere, consider use IRBuilderSourceLocRAII sourceLocInfo(getBuilder(), loc); to simplify the code. This is an RAII object that will make all future insts emited by the builder automatically have the loc as source loc, until the RAII object goes out of scope.