matchers: rename "predicate" to "satisfies"

[DartBot]

<img src="https://avatars.githubusercontent.com/u/444270?v=3" align="left" width="96" height="96"hspace="10"> Issue by seaneagan Originally opened as dart-lang/sdk#11919

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expect(5, satisfies((i) => i.isOdd));

reads better than:

expect(5, predicate((i) => i.isOdd));

[DartBot]

<img src="https://avatars.githubusercontent.com/u/5449880?v=3" align="left" width="48" height="48"hspace="10"> Comment by iposva-google

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Added Area-Pkg, Triaged labels.

[DartBot]

<img src="https://avatars.githubusercontent.com/u/5479?v=3" align="left" width="48" height="48"hspace="10"> Comment by sethladd

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Removed Type-Defect, Priority-Unassigned labels. Added Type-Enhancement, Priority-Low, PatchesWelcome, Pkg-matcher, labels.

[DartBot]

<img src="https://avatars.githubusercontent.com/u/5479?v=3" align="left" width="48" height="48"hspace="10"> Comment by sethladd

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Added Triaged label.