Clarify the license of utf8_range

[takeh1k0]

What language does this apply to?

N/A

Describe the problem you are trying to solve.

utf8_range was moved to the protobuf repository on November 9, 2023, but the license of the source code after the move is unclear.

The license file exists in the third_party/utf8_range directory, but since this directory was copied from the original repository, it is not clear if this license still applies.

Describe the solution you'd like

If the license of utf8_range has not been discussed and the license can be changed, I would like the license to be changed to the same license as protobuf .

Describe alternatives you've considered

If the current utf8_range license is identical to protobuf, the old LICENSE file should be deleted.

If it is different from the license of protobuf, it should be mentioned in the README of protobuf, etc. so that it is easy to understand.

Additional context

nothing

[zhangskz]

@acozzette Can you investigate if the license file can / should be change given the repo move, or if this needs to be documented accordingly?

[acozzette]

Unfortunately I don't think we can change the license. From what I understand, we originally forked utf8_range from another project, and as a result we don't own the full copyright.