feat: deprecated find, fold, foldM, mergeBy functions for the tree map

[datokrat]

This PR adds some deprecated function aliases to the tree map in order to ease the transition from the RBMap to the tree map.

[leanprover-community-bot]

Mathlib CI status (docs):

• ❗ Batteries/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase 0f1133fe69caddf47b5d3766888da929513917af --onto befee896b38349a51dad1627360adbab317f3192. (2025-02-11 16:46:59)
• ❗ Batteries/Mathlib CI will not be attempted unless your PR branches off the nightly-with-mathlib branch. Try git rebase 0f1133fe69caddf47b5d3766888da929513917af --onto 07b0e5b7fe596178282214a5c29f42e555bba59b. (2025-02-13 09:40:41)

[datokrat]

Cannot rebase on a nightly yet because this PR builds on top of the freshly merged tree map PR from yesterday. Will rebase as soon as possible

[TwoFX]

LGTM. Presumably you could have got away with fewer aliases since switching from Lean.RBMap to Std.DTreeMap shouldn't happen, but no harm in having the aliases.

[datokrat]

LGTM. Presumably you could have got away with fewer aliases since switching from Lean.RBMap to Std.DTreeMap shouldn't happen, but no harm in having the aliases.

There's Lake.Util.DRBMap, although I'm not sure whether external users would rely on that.