chore: v6.2.0 release preparation

[JaffaKetchup]

Readers: see https://docs.fleaflet.dev/getting-started/v7-information for info.

Cherry picked from commit 4f6b524, with minor changes to prepare for release.

DO NOT MERGE. Exists for the purpose of transparency only. v7 will be released simultaneously.

[JaffaKetchup]

Information for readers:

Due to a complex release of v6.1.0, we used a seperate branch, much like this release, and cherry picked the necessary commits. That branch was #1741.
However, due to an oversight when releasing v6.2.0, rather than merging cherry picks into a branch based off the last commit of #1741, instead it used commit ec81782, to create branch #1891
This commit included a history of some breaking changes.
This meant that v6.2.0 was inadvertently released with these breaking changes, meaning it caused projects to fail to resolve when the otherwise valid constraint of ^6.0.0 was used.
The issue has been resolved in #1893, and has been released as v6.2.1, so all projects should resolve dependencies normally, without intervention, again.
The faulty version v6.2.0 has been retracted from pub.dev to prevent accidental dependency on it, and the also incorrect tag and release for v6.1.0 and v6.2.0 has been removed from GitHub.