Trie: v5 Release Planning

[holgerd77]

Follow-up on ethereumjs/merkle-patricia-tree#111

Release planning for the next major release v5 (no date yet), please use this to add breaking changes planned for v5 as well as deprecation tasks which should be executed upon.

Note that it might make sense to combine this release with a monorepo transition if planned.

Breaking Changes

• Rename from merkle-patricia-tree to @ethereumjs/trie
• Reconsider https://github.com/ethereumjs/merkle-patricia-tree/issues/108 (removal of level dependencies or alternative solution) for integration

Deprecation Tasks

• Remove deprecated semi-private _walkTrie() and _lookupNode() methods, see this comment along Refactor WalkTrie merkle-patricia-tree#135
• Make deprecated Trie.setRoot() function private (reverted in v4.1.0 release from Base trie code documentation and function clustering merkle-patricia-tree#125 with risk of breaking being too high)

[holgerd77]

Have consolidated with #1024, will close here.