Reporting multiple warnings from a single node

[quasilyte]

Given this code:

// (A)
var x, y int
// (B)
var x int
var y int

Suppose we're going to try to match the (B) sequence.
The only way to do that is inspecting *ast.BlockStmt. But that block statement may contain several occurrences of that sequence. There is currently no way to give multiple warnings from a single node.

Either there should be a separate matcher API, or generic matcher interface must be re-designed to cover this case.