[flang] Propagate lowering options from driver.

[flang] Propagate lowering options from driver.

This commit addresses concerns raised in D129497.

Propagate lowering options from driver to expressions lowering
via AbstractConverter instance. A single use case so far is
using optimized TRANSPOSE lowering with O1/O2/O3.

bbc does not support optimization level switches, so it uses
default LoweringOptions (e.g. optimized TRANSPOSE lowering
is enabled by default, but an engineering -opt-transpose=false
option can still override this).

Differential Revision: https://reviews.llvm.org/D130204