internal/goexperiment: add "NewInliner" experiment

Add "NewInliner" to the list of Go experiments, used for enabling an
updated/improved version of the function inlining phase within the Go
compiler. 

Updates #61502.

Change-Id: I3218b3ae59a2d05156e8017cd9ee1d7b66cad031
Reviewed-on: https://go-review.googlesource.com/c/go/+/511555
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Than McIntosh <thanm@google.com>

src/internal/goexperiment/exp_newinliner_off.go

@@ -0,0 +1,13 @@
+// Copyright 2023 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Code generated by mkconsts.go. DO NOT EDIT.
+
+//go:build !goexperiment.newinliner
+// +build !goexperiment.newinliner
+
+package goexperiment
+
+const NewInliner = false
+const NewInlinerInt = 0

src/internal/goexperiment/exp_newinliner_on.go

@@ -0,0 +1,13 @@
+// Copyright 2023 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Code generated by mkconsts.go. DO NOT EDIT.
+
+//go:build goexperiment.newinliner
+// +build goexperiment.newinliner
+
+package goexperiment
+
+const NewInliner = true
+const NewInlinerInt = 1

src/internal/goexperiment/flags.go

@@ -109,4 +109,8 @@ type Flags struct {
 	// CacheProg adds support to cmd/go to use a child process to implement
 	// the build cache; see https://github.com/golang/go/issues/59719.
 	CacheProg bool
+
+	// NewInliner enables a new+improved version of the function
+	// inlining phase within the Go compiler.
+	NewInliner bool
 }