Add analyzer/fixer to suggest changing code like ImmutableArray.CreateBuilder<int>(); ... to a collection expression.

[CyrusNajmabadi]

Part of #69473.

Looks for code like:

var builder = ImmutableArray.CreateBuilder<int>();
builder.Add(0);
foreach (var y in x)
    builder.Add(y);

Goo(builder.ToImmutable());

And suggests converting to:

Goo([0, .. y]);

This PR Involves a lot of refactoring of hte current analyzer/fixers to more broadly support this scenario. Specifically, the existing 'use collection initializer' already has teh support for analyzing successive statements to see if they're complimentary with a collection-initializer/expression.

But we needed to extract out pieces as that analyzer/fixer assumes you have an initial collection of hte form new Collection<int>(), and it also assumes you're replacing the intitial declaration point (whereas with builders you want to update the place where builder.ToXXX() is called.