feat(Combinatorics/SimpleGraph): Provide iff statements for distance equal and greater than 2

[Rida-Hamadani]

I need these lemmas to prove that Moore graphs of girth 5 are strongly regular.

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• [ ] depends on: #11945

[leanprover-community-mathlib4-bot]

This PR/issue depends on:

• ~~leanprover-community/mathlib4#11945~~ By Dependent Issues (🤖). Happy coding!

[github-actions[bot]]

PR summary f8cbb59b38

Import changes for modified files

No significant changes to the import graph

Import changes for all files

Files	Import difference

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Declarations diff

+ Reachable.of_dist_ne_zero + dist_eq_one_iff_adj + dist_eq_two_iff + dist_ne_zero_iff_ne_and_reachable + exists_walk_of_dist_ne_zero + two_lt_dist_iff

You can run this locally as follows

## summary with just the declaration names:
./scripts/declarations_diff.sh <optional_commit>

## more verbose report:
./scripts/declarations_diff.sh long <optional_commit>

The doc-module for script/declarations_diff.sh contains some details about this script.