Updated TupleExpr's getSourceRange to inspect child elements source ranges

[mxswd]

In a TupleExpr, if the parens are both invalid, then you can only have a
valid range iff both the first element and last element have valid ranges.
Source ranges also have the property:
  Start.isValid() == End.isValid()
For example, given the buffer "one", of the form:
(tuple_expr
  (declref_expr range=[test.swift:1:0 - line:1:2] ...)
  (declref_expr range=invalid ...))
the range of this TupleExpr is SourceLoc() (invalid).
      v invalid                v invalid
      (     one,         two   )
      valid ^    invalid ^
COL:  xxxxxx012xxxxxxxxxxxxxxxxx
but the SourceRange of 'one' is 1:0 - 1:2.

Also added triple and quadruple tests.

[mxswd]

@jrose-apple thoughts?

[jrose-apple]

Looks good. Can you add a test for a tuple of all-invalid-location elements?

[mxswd]

Yup sure thing.

[mxswd]

I do already have a test for a tuple of invalid source ranges.

SmallVector<Expr *, 2> subExprsInvalid({ two, three });
SmallVector<Identifier, 2> subExprNamesInvalid(2, Identifier());
auto allInvalid = TupleExpr::createImplicit(C.Ctx, subExprsInvalid, subExprNamesInvalid);

But I did notice I had a typo in one of the strings.

[jrose-apple]

Ah, whoops. Sorry to miss that.

[jrose-apple]

@swift-ci Please smoke test and merge

[jrose-apple]

@swift-ci Please smoke test and merge