Two fixes to capture checking

[Linyxus]

• It changes isParamDependent to consider CaptureDependency as well, so that when applying a capture dependent function the capture sets in the types of the remaining parameters will be correctly substituted. For example:

def foo[X](x: Foo[X]^, op: () ->{x} Unit): Unit = ???
foo(a, useA)

After rechecking a in the argument list, the expected type of the second argument, useA, should become () -> {a} Unit. This example previously does not work.

• It fixes Dependent function application can leak a scoped capability #17517. It fixes the healing of capture sets, which happens at the end of the capture checking phase, in which we traverse the capture checked tree and try to heal the ill-formed capture sets in type arguments. Here we say a capture set C in a type argument is ill-formed if it contains TermParamRef bound by other lambdas. For example:

def usingLogger[sealed T](f: OutputStream^)(op: Logger^{f} => T): T = ???
usingLogger[() ->?1 Unit](file)(l => () => l.log("test"))

l will be propagated to ?1 as a result of capture checking, which makes ?1 ill-formed and we should widen l to file. The problem is that we heal the capture sets one-after-another but the healing of a later capture set may propagate more TermParamRefs to a healed one. For example:

usingFile[() ->?2 Unit](  // should be error
  "foo",
  file => {
    usingLogger[() ->?1 Unit](file)(l => () => l.log("test"))
  }
)

After capture checking both ?1 and ?2 will be {l}. When traversing the tree we first heal ?2, wherein we widen l to file, but file is a TermRef here and we do nothing. Then, only later when we heal ?1, we also widen l to file but this will end up propagating a TermParamRef of file to ?2, which we should have widened as well. But ?2 is already healed and is not inspected again.

This PR solves this issue by installing a handler when healing the capture sets which will try to heal the new elements propagated later in the healing process.