Update clang-format to handle `[unroll]` when editing HLSL

[farzonl]

clang-format doesn't seem to handle [unroll], but this should probably be one of:

  [unroll]
  for (int i = 1; i < N; ++i)
    XSquaredSum += XSquared[i];

or

  [unroll] for (int i = 1; i < N; ++i)
    XSquaredSum += XSquared[i];

The latter is closer to what clang-format does with [[unroll]] instead of [unroll] to trick it into seeing that as an attribute.

Originally posted by @bogner in #121611 (comment)

[llvmbot]

@llvm/issue-subscribers-clang-format

Author: Farzon Lotfi (farzonl)

clang-format doesn't seem to handle `[unroll]`, but this should probably be one of: ```c++ [unroll] for (int i = 1; i < N; ++i) XSquaredSum += XSquared[i]; ``` or ```c++ [unroll] for (int i = 1; i < N; ++i) XSquaredSum += XSquared[i]; ```

The latter is closer to what clang-format does with [[unroll]] instead of [unroll] to trick it into seeing that as an attribute.

Originally posted by @bogner in #121611 (comment)

[damyanp]

Estimate here assumes that we have a working HLSL mode.