Simple ota and ldo

[sehuang]

Migrating the simple OTA and LDO generators I made for the May 2023 PLL instance to bag3_analog.

[boblinchuan]

@sehuang Can you redo this PR with [49042ca](https://github.com/ucb-art/bag3_analog/pull/17/commits/49042ca316e280c8c50d3a1c89434a9a7b4c445f) as the starting commit? The commits prior to that have all been merged in already.

[sehuang]

@sehuang Can you redo this PR with [49042ca](https://github.com/ucb-art/bag3_analog/pull/17/commits/49042ca316e280c8c50d3a1c89434a9a7b4c445f) as the starting commit? The commits prior to that have all been merged in already.

Oops, I did a merge rather than a rebase. I can redo this as a rebase if you want to preserve the commit history prior to this merge.

It's been a long time since I made this PR, so some of the updates in the RDAC decoder you might want to double check again to make sure they still make sense. I made a hack to res_ladder for sky130 that I explicitly excluded from this PR so it doesn't pollute the upstream generator, but still good to have a second look-over by someone else.