Add ToolPathResolver.TryFindPathExecutable

### Description

As we also use Fallout targets for local development, I sometimes want to first check if some tool is available and then try something else, or provide a friendly message. E.g. `ToolPathResolver.GetPathExecutable("func")` will throw if the Azure Functions Core Tools aren't installed.

### Usage Example

`bool ToolPathResolver.TryGetPathExecutable(string tool, out string path)`

### Alternative

N/a/

### Could you help with a pull-request?

Yes

Locate ToolPathResolver and its existing GetPathExecutable implementation, then check how it handles unavailable tools. Resolve the TryFindPathExecutable versus TryGetPathExecutable naming discrepancy, add the requested non-throwing lookup with the stated out-path behavior, and verify found and missing-tool cases.

Written by the indexing model from the issue text.