Clarify whether any glob patterns are invalid, and the behaviour if a client receives an invalid glob

An issue came up in Neovim at https://github.com/neovim/neovim/issues/37204 about it failing to initialize if the server provides a glob like **/**.dart which it considers to be invalid.

It's not clear to me from the spec that **/**.dart is invalid (it might not be what was intended, but that's a different issue), or what the behaviour should be if a client receives an invalid glob (if that is possible). My suggestion is that neovim handles this the same way that npm's glob/minimatch does, but I also appreciate that they should be following a spec and not another implementation.

Specifically, the should make it clear:

• whether **/**.dart is valid or not
  • and what its behaviour would be
• whether unclosed braces/brackets are valid or not, for example example.[0-9 missing its closing bracket or **​/*.{ts,js missing its closing brace
  • and what their behaviour should be
• if a pattern is invalid, what the behaviour should be (fail, ignore, etc.)

Start with the glob-pattern wording in the language server protocol and compare it with the Neovim issue and the npm glob/minimatch behavior mentioned here. Clarify whether the listed patterns are valid, define their behavior, and specify how clients should handle invalid patterns.