Add documentation for Metal target

[swoods-nv]

Support for Metal should be documented as in prototype stage. Documentation must be added to docs/user-guide/09-targets.md to indicate that Metal is available as a work in progress (e.g. see note below CUDA and OptiX section). Additionally, it would be nice to document the format of the profile strings used by findProfile() in the appropriate places in docs/user-guide/08-compiling.md

[swoods-nv]

Want to land before SIGGRAPH, but not critical for EOQ2

[swoods-nv]

There's more detailed documentation needed here than I'd realized-- I'm going to need one of the authors of the Metal backend to assist. @ArielG-NV @jkwak-work @csyonghe

[ArielG-NV]

it would be nice to document the format of the profile strings used by findProfile() in the appropriate places in docs/user-guide/08-compiling.md

We also should allow a user to choose the metal version being compiled with if we are to add findProfile documentation for all targets (otherwise profiles are quite useless with metal)

[jkwak-work]

it would be nice to document the format of the profile strings used by findProfile() in the appropriate places in docs/user-guide/08-compiling.md

We also should allow a user to choose the metal version being compiled with if we are to add findProfile documentation for all targets (otherwise profiles are quite useless with metal)

@ArielG-NV , do we have a way to dump the name strings of profiles?
As far as I can see, there isn't a way to do it currently.

Since there are a lot of profile names, I don't think we can list all of them on the document.
We should refer to a command-line option that can print out all the available profile name strings.

[ArielG-NV]

@ArielG-NV , do we have a way to dump the name strings of profiles?
As far as I can see, there isn't a way to do it currently.

There currently is no way todo this.

Since there are a lot of profile names, I don't think we can list all of them on the document.
We should refer to a command-line option that can print out all the available profile name strings.

I believe we could do both options.

The idea I have in mind for documenting every capability/profile:

1. inside tools\slang-capability-generator\capability-generator-main.cpp we could add logic to require a /// comment above the line with the definition of a capability.
2. store this string inside slang\build\source\slang\capability\slang-generated-capability-defs-impl.h.
3. Add build step to Slang (or CI) to autogenerate a user-doc with all capabilities using slang\build\source\slang\capability\slang-generated-capability-defs-impl.h
4. output the auto-generate code from '.3' as a a command-line output with slangc if slangc -help capabilities is added (or something similar)

Related issue: #4125

[swoods-nv]

Metal documentation is still very incomplete.