[bazel] Add support for multiple tblgen outputs

[keith]

Required after #167700

This adds yet another format for tbl_outs where you pass the list of opts, and a list of outputs (where previously you could only have 1 output). In that case all outputs must be produced, but the first is used for the -o arg since tblgen is generating the other names based on that single argument.

[keith]

this doesn't work as is because the case where this is used today writes #includes to the file that are relative to bazel-bin and are not valid later on without some more includes / strip_include_prefix usage

[keith]

big reformat change here required by buildifier, but this was an automated swap from dictionary to the tuple format

[keith]

i think that we'll need to do something smarter for tblgen's #include path creation since right now it looks like this:

#include "bazel-out/cfg/bin/external/+llvm_configure+llvm-project/llvm/lib/Target/AMDGPU/R600GenRegisterInfoTargetDesc.inc"

but likely we want this:

#include "llvm/lib/Target/AMDGPU/R600GenRegisterInfoTargetDesc.inc"

i think the assumption was the latter path would also match the argument to tblgen itself, and that assumption doesn't hold with bazel

[keith]

this works after #168409

[pranavk]

@keith we are very interested in getting this merged.

Just to make sure we are on same page. After #168409, this PR should be able to fix the broken bazelbot. No other pending issues, right?

[keith]

now #168355 instead but yes hopefully. i imagine something else broke on the bazel side in between, but likely just easy import changes vs something more complex like this. i will land it as soon as that one is in and then fix forward anything else