When EOpIndexDirect/EOpIndexIndirect/EOpIndexDirectStruct/TIntermSwizzle
appear in [] in ssbo access chain, we should transfer the process of them to
OutputHLSL.

For example:
    instance.v[gl_GlobalInvocationID.x] = data;
    // becomes
    float_Store(dx_instance, 0 + 16 * gl_GlobalInvocationID.x, _data);

    instance.v[s.index[0].x] = data;
    // becomes
    float_Store(dx_instance, 0 + 16 * _s.index[0].x, _data);

Bug: angleproject:1951
Change-Id: I333e238400a10a799a6294f8759cf9c4ef2451c8
Reviewed-on: https://chromium-review.googlesource.com/c/1250661Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Jiajia Qin <jiajia.qin@intel.com>