[ET-VK][ez] Fix 8 bit linear compute shader dispatch

## Context


Currently, for the `q_8w_linear` shader, both the texture and the buffer variants use the same global work group and local work group setting.

Specially, the global work group is set to `{out.numel(), 1, 1}` and the local work group is set to `{64, 1, 1}`.

However, I believe this results in a very poor memory re-use for the texture shader. In this configuration:

* Within a work group each invocation will be requesting a different row of A - 64 rows of A requested in total
* All work groups will be requesting the same row of B
* One work group will load 65 unique rows from A and B

Compare this to a local work group size of `{8, 8, 1}`

* Across the work group, 8 rows will be loaded from A and 8 rows will be loaded from B
* One work group will load 16 unique rows total from A and B

Evidently, there is better memory re-use in the latter work group as fewer unique rows are loaded.

## Changes

Modify the `q_8w_linear` shader to use `{8, 8, 1}` local wg if possible. If `M` is small, then instead use `{4, 16, 1}` or `{2, 32, 1}` to reduce the number of inactive invocations.

Differential Revision: [D71706489](https://our.internmc.facebook.com/intern/diff/D71706489/)

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