AST Matcher library

[TristonianJones]

Use CEL to match CEL AST fragments

The idea is to build upon CEL's very fast Pratt parser to provide AST match capabilities with capture expressions:

// Match a call with 1 fixed argument and between 0 and 2 trailing arguments
<call_name>(_1, _2.atLeast(0).atMost(2))
// Match a call with 1 fixed argument and at least 1 trailing argument
<call_name>(_1, _2.atLeast(1))
// Match a call with 1 fixed argument and an optional trailing argument
<call_name>(_1, _2.optional())
// Match variadic function calls with zero or more trailing arguments
concat(_1, _2.star())
// Match a list with exactly two leading elements followed by zero or more tail elements
[_1.repeated(2), _2.star()]
// Match a list with at least one element
[_1.atLeast(1)]