CreateIndex: Move Display fmt to struct

[philipcristiano]

Move the Display trait fmt implementation to the CreateIndex struct to to allow for display!

The struct was created in a0f511c with the CreateTable fmt being moved, but the CreateIndex was not.

Follows up from #1291

[coveralls]

Pull Request Test Coverage Report for Build 9467753604

Details

• 25 of 27 (92.59%) changed or added relevant lines in 2 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+0.004%) to 88.882%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/ast/dml.rs	24	26	92.31%

Files with Coverage Reduction	New Missed Lines	%
src/ast/mod.rs	1	81.5%

Totals
Change from base Build 9439708625:	0.004%
Covered Lines:	26254
Relevant Lines:	29538

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💛 - Coveralls

[jmhain]

lgtm, cc @alamb

[alamb]

nice -- thank you @philipcristiano and @jmhain