cogl: Mark exported cogl symbols using COGL_EXPORT

Just like libmutter-clutter, and libmutter, mark exported symbols with
an COGL_EXPORT macro. This removes the .map and .map.in files previously
used, containing a list of semi private symbols. This symbol was out of
date, i.e. pointed to non-existing symbols, and was also replaced with
COGL_EXPORT macros.

unit_test_* symbols are exported by the help of the unit test defining
macro. test_* symbols are no longer supported as it proved unnecessary.

GNOME/mutter!1059
5 jobs for !1059 with wip/cogl-symbol-visibility-cleanup in 12 minutes and 43 seconds (queued for 1 second)
detached
Status Job ID Name Coverage
  Review
passed #642421
check-commit-log

00:00:34

 
  Build
passed #642422
build-mutter

00:07:37

passed #642423
build-without-native-backend-and-wayland

00:01:35

 
  Test
passed #642425
can-build-gnome-shell

00:02:19

passed #642424
test-mutter

00:04:31