All other tablegen files in this directory have the license header, but
`Common.td` is missing it

This adds a new device info query for the maximum workgroup/block size
for each dimension.

GenericKernelTy has a pointer to the name that was used to create it.
However, the name passed in as an argument may not outlive the kernel.
Instead, GenericKernelTy now contains a std::string, and copies the
name into there.

- Update the main README to reflect the current project status
- Rework the main API generation documentation. General fixes/tidying,
but also spell out explicitly how to make API changes at the top of the
document since this is what most people will care about.

---------

Co-authored-by: Martin Grant <martingrant@outlook.com>

Added GPU test job limit to make it consistent with current config
https://github.com/llvm/llvm-zorg/blob/main/buildbot/osuosl/master/config/builders.py#L2027C31-L2027C77

Summary:
This adds a basic outline for adding 'conformance' tests. These are
tests that are intended to check device code against a standard. In this
case, we will expect this to be filled with math conformance tests to
make sure their results are within the ULP requirements we demand.

Right now this just *assumes* the GPU libc is there, meaning you'll
likely need to do a manual `ninja` before doing `ninja -C
runtimes/runtimes-bins offload.conformance`.

Fix a couple of unhandled edge cases in offload-tblgen that were found
by static analysis
* `LineStart` may wrap around to 0 when processing multi-line strings.
The value is not actually being used in that case, but still better to
explicitly handle it
* Possible unchecked nullptr when processing parameter flags

closes https://github.com/llvm/llvm-project/issues/144786

This makes several small changes to how the platform and device info
queries are handled:
* ReturnHelper has been replaced with InfoWriter which is more explicit
  in how it is invoked.
* InfoWriter consumes `llvm::Expected` rather than values directly, and
  will early exit if it returns an error.
* As a result of the above, `GetInfoString` now correctly returns errors
  rather than empty strings.
* The host device now has its own dedicated "getInfo" function rather
  than being checked in multiple places.

`olShutDown` was not properly calling deinit on the platforms, resulting
in random segfaults on AMD devices.

As part of this, `olInit` and `olShutDown` now alloc and free the
offload context rather than it being static. This
allows `olShutDown` to be called within a destructor of a static object
(like the tests do) without having to worry about destructor ordering.