Add ssreflect to the prelude

[proux01]

This adds ssreflect to the prelude (split out of #21478)

Depends on: #21478 (merged)

• Added / updated test-suite.

• Added changelog.
• Added / updated documentation.
  • Documented any new / changed user messages.
  • Updated documented syntax by running make doc_gram_rsts.

Overlays (to be merged before the current PR)

• Adapt to https://github.com/rocq-prover/rocq/pull/21478 thery/coqprime#93 (edit 8 lines, renaming some tactic rw -> rew)
• Adapt to https://github.com/rocq-prover/rocq/pull/21478 mit-plv/coqutil#149 (edit 2 lines, adding parentheses)
• Adapt to https://github.com/rocq-prover/rocq/pull/21478 mit-plv/fiat#127 (edit 4 lines, adding parentheses)
• Adapt to https://github.com/rocq-prover/rocq/pull/21478 mit-plv/kami#46 (edit 1 line, adding parentheses)
• Adapt to https://github.com/rocq-prover/rocq/pull/21478 damien-pous/relation-algebra#53 (edit 5 lines, adding parentheses)
• Adapt to https://github.com/rocq-prover/rocq/pull/21478 stdlib#228 (edit 1 line, adding a space // -> / /)