LSP regex handling inconsistent with YANG RFC

[esmasth]

A YANG pattern "[a-zA-Z0-9!$%\\^()\\[\\]_\\-~{}.+]*" is flagged as type-error. As a second opinion CESNET/libyang yangre tool as well as mbj4668/pyang were used to check whether the regex is consistent, and it was found to be acceptable. Possibly need adjustment to regex handling in yang-lsp.

[esmasth]

Possibly same underlying root cause as #227

Changing "[a-zA-Z0-9!$%\\^()\\[\\]_\\-~{}.+]*" to '[a-zA-Z0-9!$%\^()\[\]_\-~{}.+]*' makes the error go away.