[dev.typeparams] cmd/compile/internal/syntax: prepare syntax nodes for type parameters

- add TParamList fields to TypeDecl, FuncDecl
- also: change File.Lines to File.EOF so we have the actual file end position

Change-Id: Ia345f888080a884f7ac5cefd8bff3d80e4a59cdc
Reviewed-on: https://go-review.googlesource.com/c/go/+/261657
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

src/cmd/compile/internal/syntax/parser_test.go

@@ -76,7 +76,7 @@ func TestStdLib(t *testing.T) {
 				if *verify {
 					verifyPrint(filename, ast)
 				}
-				results <- parseResult{filename, ast.Lines}
+				results <- parseResult{filename, ast.EOF.Line()}
 			})
 		}
 	}()