gitlab-ci: consolidate release and package job infrastructure

Use `linux_release` in names associated with building or testing
release-style binaries.  Add a `.linux_package` helper to adjust
the release binary build behavior for package-specific jobs.
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 680d77b..b4bc718 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -93,8 +93,8 @@
 
 build:centos6-release:
     extends:
-        - .release_linux
-        - .cmake_build_release_linux
+        - .linux_release_x86_64
+        - .cmake_build_linux_release
         - .cmake_release_artifacts
         - .linux_builder_tags
         - .run_manually
@@ -102,7 +102,7 @@
 test:debian10-ninja:
     extends:
         - .debian10_ninja
-        - .cmake_test_linux_package
+        - .cmake_test_linux_release
         - .linux_builder_tags_qt
         - .run_dependent
     dependencies:
@@ -113,7 +113,7 @@
 test:fedora33-makefiles:
     extends:
         - .fedora33_makefiles
-        - .cmake_test_linux_package
+        - .cmake_test_linux_release
         - .linux_builder_tags_qt
         - .run_dependent
     dependencies:
@@ -124,7 +124,7 @@
 test:cuda10.2-nvidia:
     extends:
         - .cuda10.2_nvidia
-        - .cmake_test_linux_package
+        - .cmake_test_linux_release
         - .linux_builder_tags_cuda
         - .run_dependent
     dependencies:
@@ -165,8 +165,9 @@
 
 build:linux-x86_64-package:
     extends:
-        - .linux_package_x86_64
-        - .cmake_build_linux_package
+        - .linux_package
+        - .linux_release_x86_64
+        - .cmake_build_linux_release
         - .cmake_release_artifacts
         - .linux_builder_tags
         - .run_only_for_package
@@ -188,8 +189,9 @@
 
 build:linux-aarch64-package:
     extends:
-        - .linux_package_aarch64
-        - .cmake_build_linux_package
+        - .linux_package
+        - .linux_release_aarch64
+        - .cmake_build_linux_release
         - .cmake_release_artifacts
         - .linux_builder_tags_aarch64
         - .run_only_for_package