Add SyntaxError#path

[wasabigeek]

Attempt for [easy, java] SyntaxError#path has been added. [Feature #19138] as part of #3039.

There's already a sourceLocation in RubySyntaxError, which I believe is used to generate the message with filename: https://github.com/shopify/truffleruby/blob/add-syntaxerror-path/src/main/java/org/truffleruby/core/exception/CoreExceptions.java#L1015. This PR exposes that sourceLocation's filename directly (I think) as #path.

The original also has some handling for an existing SyntaxError's path being changed (diff), not sure if I needed to handle that.

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[thomasmarshall]

I noticed a small difference between MRI and the implementation here. When instantiating the error directly, in MRI the path method returns nil but with this change in TruffleRuby it returns "(unknown)". Maybe there could be a test similar to this one for LoadError :

truffleruby/spec/ruby/core/exception/load_error_spec.rb

Lines 8 to 10 in 5522b6a

	it "is nil when constructed directly" do
	@le.path.should == nil
	end

[eregon]

Good point, I think CRuby never uses (unknown) or similar, so let's return nil in that case.
@wasabigeek Could you do that?

[wasabigeek]

This is to handle RubyString / Nil - a brief search of the codebase suggested that this was how we handled varying return types, did I miss something?

[andrykonchin]

This is correct. Looks great!

[andrykonchin]

Could you please squash working commits?

[wasabigeek]

@andrykonchin squashed! 🙇