feat(editor): add syntax highlighting for go.mod and go.work files (#1695)

go.mod and go.work opened as plain text: their language definitions had no ui-mode, so no CodeMirror language loaded. Add a GoMod mode (a small stream parser): directives as keywords, module paths as strings, versions as numbers, // comments; shared by go.mod and go.work.

Co-authored-by: elfadl <[email protected]>

languages/gomod.toml

@@ -3,6 +3,7 @@ name = "Go Module"
 filenames = ["go.mod"]
 line-comment = "//"
 indent = { tab-size = 4, insert-spaces = false }
+ui-mode = "GoMod"
 
 [[language-servers]]
 name = "gopls"

languages/gowork.toml

@@ -3,6 +3,7 @@ name = "Go Workspace"
 filenames = ["go.work"]
 line-comment = "//"
 indent = { tab-size = 4, insert-spaces = false }
+ui-mode = "GoMod"
 
 [[language-servers]]
 name = "gopls"