gen,checker: implement g.trace/2 and c.trace/2, similar to p.trace/2

vlib/v/ast/ast.v

@@ -469,7 +469,8 @@ pub:
 // That array is then passed to V's checker.
 pub struct File {
 pub:
-	path         string // path of the source file
+	path         string // absolute path of the source file - '/projects/v/file.v'
+	path_base    string // file name - 'file.v' (useful for tracing)
 	mod          Module // the module of the source file (from `module xyz` at the top)
 	global_scope &Scope
 pub mut:

vlib/v/checker/checker.v

@@ -5298,3 +5298,9 @@ fn (mut c Checker) verify_all_vweb_routes() {
 		}
 	}
 }
+
+fn (mut c Checker) trace(fbase string, message string) {
+	if c.file.path_base == fbase {
+		println('> c.trace | ${fbase:-10s} | $message')
+	}
+}

vlib/v/gen/cgen.v

@@ -5850,3 +5850,9 @@ pub fn get_guarded_include_text(iname string, imessage string) string {
 	'.strip_margin()
 	return res
 }
+
+fn (mut g Gen) trace(fbase string, message string) {
+	if g.file.path_base == fbase {
+		println('> g.trace | ${fbase:-10s} | $message')
+	}
+}

vlib/v/parser/parser.v

@@ -232,6 +232,7 @@ pub fn (mut p Parser) parse() ast.File {
 	//
 	return ast.File{
 		path: p.file_name
+		path_base: p.file_base
 		mod: module_decl
 		imports: p.ast_imports
 		imported_symbols: p.imported_symbols