Update tsconfig to match current node version

[mrgrain]

jsii 5.3+ only supports Node 18+ (and has been for a while).

We should match the default tsconfig (lib, target, module) to match the recommended settings from the TypeScript project
https://github.com/microsoft/TypeScript/wiki/Node-Target-Mapping#node-18

(jsii 5.2 supports Node16, so this should not be backported or we should use the older settings)

We can only change these in new minor versions, otherwise it's breaking (particularly module).