Transforms the diagnostic severity from the LexingDiagnosticSeverity format to LSP's DiagnosticSeverity format.
DiagnosticSeverity
The lexing diagnostic severity
Diagnostic severity according to vscode-languageserver-types/lib/esm/main.js#DiagnosticSeverity
vscode-languageserver-types/lib/esm/main.js#DiagnosticSeverity
Transforms the diagnostic severity from the LexingDiagnosticSeverity format to LSP's
DiagnosticSeverityformat.