zink: flush pending clears for fb texture barriers

zink: flush pending clears for fb texture barriers

if a texture barrier occurs while clears are pending, these clears should
show up if the fb attachments are read in shaders, so trigger a renderpass
to flush out the clears

cc: mesa-stable

fixes #6766

fixes (radv):
dEQP-GLES3.functional.draw_buffers_indexed.overwrite_common.common_advanced_blend_eq_buffer_advanced_blend_eq
dEQP-GLES3.functional.draw_buffers_indexed.overwrite_common.common_blend_eq_buffer_advanced_blend_eq
dEQP-GLES3.functional.draw_buffers_indexed.overwrite_common.common_separate_blend_eq_buffer_advanced_blend_eq
dEQP-GLES3.functional.draw_buffers_indexed.overwrite_indexed.common_advanced_blend_eq_buffer_advanced_blend_eq
dEQP-GLES3.functional.draw_buffers_indexed.overwrite_indexed.common_advanced_blend_eq_buffer_blend_eq
dEQP-GLES3.functional.draw_buffers_indexed.overwrite_indexed.common_advanced_blend_eq_buffer_separate_blend_eq

Reviewed-By: Tatsuyuki Ishi <ishitatsuyuki@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/17363>