Fix spurious "Lexical argument shadows the dynamic variable" due to inlining

Before this patch doing:

    rm lisp/calendar/calendar.elc
    make lisp/calendar/cal-hebrew.elc

would spew out lots of spurious such warnings about a `date` argument,
pointing to code which has no `date` argument in sight.  This was
because that code had calls to inlinable functions (taking a `date`
argument) defined in `calendar.el`, and while `date` is a normal
lexical var at the site of those functions' definitions, it was
declared as dynbound at the call site.

* lisp/emacs-lisp/byte-opt.el (byte-compile-inline-expand):
Don't impose our local context onto the inlined function.

* test/lisp/emacs-lisp/bytecomp-tests.el: Add matching test.

test/lisp/emacs-lisp/bytecomp-resources/nowarn-inline-after-defvar.el

@@ -0,0 +1,17 @@
+;; -*- lexical-binding: t; -*-
+
+;; In this test, we try and make sure that inlined functions's code isn't
+;; mistakenly re-interpreted in the caller's context: we import an
+;; inlinable function from another file where `foo-var' is a normal
+;; lexical variable, and then call(inline) it in a function where
+;; `foo-var' is a dynamically-scoped variable.
+
+(require 'foo-inlinable
+         (expand-file-name "foo-inlinable.el"
+                           (file-name-directory
+                            (or byte-compile-current-file load-file-name))))
+
+(defvar foo-var)
+
+(defun foo-fun ()
+  (+ (foo-inlineable 5) 1))