Adding construction contexts is easy. This patch builds on top of D42672 to add construction contexts for constructors that are direct initializers (without any ExprWithCleanups wrappers - but those would need to be covered later) of variable DeclStmts.
The analyzer still doesn't use them, and existing construction contexts are not yet enough as a drop-in replacement for existing mechanisms in the analyzer.
I should probably make some sort of scope guard later - that'd push the construction context on the stack when it gets constructed and pop it when it is destroyed.