gRPC Swift 1.20.0

SemVer Minor

• Drop support for Swift 5.6 (#1657)
• Make the connection pool error public (#1685)
• Allow binding to a socket address via the server builder (#1686)
• Add convenience methods to keepalive to jitter the interval (#1697)

SemVer Patch

• Switch to swift-format and re-format (#1655)
• Add missing deque import (#1670)
• Add support for package visibility modifier to the code generator (#1674)
• Additional keepalive diagnostics (#1692)
• Fix last peer initiated stream ID when quiescing (#1700)
• Bump version number to 1.20.0 (#1701)

Other Changes

• Fix soundness script (#1676)
• Multiple changes in preparation to support the reflection service (#1675,
  #1695, #1659, #1677, #1680, #1682, #1669, #1654)
• Multiple changes working towards v2 (#1652, #1656, #1660, #1664, #1665, #1666, #1667, #1668, #1671, #1672, #1678, #1681, #1683, #1684, #1687, #1688, #1689, #1690, #1691, #1693, #1696, #1698)