Fix bridge generation when erased precedes a non-erased parameter

[tanishiking]

Fixes #25726.

The following crashed during erasure with
"assertion failed: bad adapt for this.run(): (x$0: Int): String":

class Ev
trait Svc[A]:
  def run(using erased Ev)(a: A): String
class ISvc extends Svc[Int]:
  def run(using erased Ev)(a: Int): String = a.toString

Since A is specialized to Int, the post-erasure signatures of the parent ((a: Object): String) and the child ((a: Int): String) differ, so a bridge method is generated in ISvc.

However, while bridge body has application based on post-erasure arguments, Erasure's typer expected bridge method to have pre-erasure form:

For example,
Bridges.bridgeRhs built a single flat Apply(this.run, [a]) one argument list, that matches the post-erasure method shape.

On the other hand, Erasure.Typer.typedApply re-types the tree using the pre-erasure type (ev: Ev)(a: A): String and filters out arguments in erased slots. For the bridge function, it mistook a for the erased slot, and drop it.
As a result, the Apply become something like this.run() and adaptToType failed on the dangling ``
The Apply became this.run() and `adaptToType` failed.

The same mismatch breaks every shape where erased appears before a non-erased parameter:

(using erased Ev)(a: A)
(erased x, y)
(erased x, y)(z)

This commit fixes the problem by:

(1) Now, bridgeRHS reconstructs the pre-erasure list shape in .applyMemberArgs.
For each pre-erasure parameter list we emit nested Applys
that contains only that list's non-erased arguments.
(2) For bridge, we attach Erasure.PostErasureArgs to those Applys,
that represents all args in the list are non-erased args.
Erasure.Typer.typedApply skips its erased-argument filter when
that attachment is there (because the args are already in
post-erasure form).

For (using erased Ev)(a: A) the bridge produces

Apply(Apply(this.run, []), [a])
// instead of Apply(this.run, [a])

How much have you relied on LLM-based tools in this contribution?

Extensively for problem investigation, minimally for writing code.

How was the solution tested?

testCompilation i25726