Flexible fixed, optional and named argument method signatures

[DartBot]

This issue was originally filed by @rbishop-bah

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This is a suggestion for consideration for Dart 2.0

I'd like to be able to do something like this:

myMethod(dynamic a, [String b], {num q, num r, num s}, Point p, {String str}, [num z], List aList) {...}

I'd like to be able to combine fixed, optional and optional-named arguments in any combination I think is appropriate for the method I'm writing and have the analyzer/compiler/editor enforce the use of proper signatures.

myMethod("a", "b", r:7, point, str:"hello", 12, []);
myMethod("a", q:7, r:5, point, [11]);
myMethod("a", point, str:"goodbye", null);

all valid. Etc. Many combinations possible.

Issue #7056 is similar.

[sethladd]

Removed Type-Defect label.
Added Type-Enhancement, Area-Language, Triaged labels.

[gbracha]

I'll mark this as a duplicate of 7056. Note that you will never be able to mix required and optional positionals in arbitrary order.

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Added Duplicate label.
Marked as being merged into #7056.