go/token: add (*FileSet).RemoveFile(*File) method
The design of FileSet encourages it to be used as a global variable.
Each call to AddFile consumes about 3KB, that is never returned,
even after an application no longer cares about the File.
This change adds a RemoveFile method that a long-running application
can use to release a File that is no longer needed, saving memory.
Fixes golang/go#53200
Change-Id: Ifd34d650fe0d18b1395f922a4cd02a535afbe560
Reviewed-on: https://go-review.googlesource.com/c/go/+/410114
Auto-Submit: Alan Donovan <adonovan@google.com>
Run-TryBot: Alan Donovan <adonovan@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>