3bb6c73f2d Add methods to retrieve inner types (Shing Him Ng)
Pull request description:
Resolves#4345
ACKs for top commit:
tcharding:
ACK 3bb6c73f2d
apoelstra:
ACK 3bb6c73f2d3edd1165b7b7f3a833fa471786e166; successfully ran local tests; should backport to 0.32.x
Tree-SHA512: c89017bbc2126ec62c756c4ee9b49dcc8b94a3063a8155aadcf7c69a6f0bc9337baedffe7f52a4ab6f0b738302bea683391d394483c4c7eefbb622b97d34d26c