Hide commands intended as command variables

The commands `bazel.info.*` and `bazel.getOutputPath` are intended to be
used as command variables within `launch.json` and `task.json`. For
additional context, see  bazel-contrib#273, bazel-contrib#275 and bazel-contrib#291.

Those commands are not intended to be called by users directly. As such,
they should not show up in the command palette. Calling them from the
command picker has no user-visible effect and leaves the user with the
impression that those commands would be broken.

This commit removes them from the `commands` contribution point, thereby
hiding them from the command picker. To make sure that the extension is
loaded as soon as some `task.json`/`launch.json` invokes any of those
commands, they now need to be registered as `activationEvents`, since VS
Code will no longer discover those events automatically from the
`commands` contributions.

package.json

@@ -21,7 +21,14 @@
         "workspaceContains:**/WORKSPACE",
         "workspaceContains:**/WORKSPACE.bazel",
         "workspaceContains:**/MODULE.bazel",
-        "workspaceContains:**/REPO.bazel"
+        "workspaceContains:**/REPO.bazel",
+        "onCommand:bazel.getTargetOutput",
+        "onCommand:bazel.info.bazel-bin",
+        "onCommand:bazel.info.bazel-genfiles",
+        "onCommand:bazel.info.bazel-testlogs",
+        "onCommand:bazel.info.execution_root",
+        "onCommand:bazel.info.output_base",
+        "onCommand:bazel.info.output_path"
     ],
     "main": "./out/src/extension/extension",
     "contributes": {
@@ -90,41 +97,6 @@
                 "command": "bazel.copyTargetToClipboard",
                 "title": "Copy Label to Clipboard"
             },
-            {
-                "category": "Bazel",
-                "command": "bazel.getTargetOutput",
-                "title": "Get output path for the given target"
-            },
-            {
-                "category": "Bazel",
-                "command": "bazel.info.bazel-bin",
-                "title": "Get bazel-bin value"
-            },
-            {
-                "category": "Bazel",
-                "command": "bazel.info.bazel-genfiles",
-                "title": "Get bazel-genfiles value"
-            },
-            {
-                "category": "Bazel",
-                "command": "bazel.info.bazel-testlogs",
-                "title": "Get bazel-testlogs value"
-            },
-            {
-                "category": "Bazel",
-                "command": "bazel.info.execution_root",
-                "title": "Get Bazel execution_root value"
-            },
-            {
-                "category": "Bazel",
-                "command": "bazel.info.output_base",
-                "title": "Get Bazel output_base value"
-            },
-            {
-                "category": "Bazel",
-                "command": "bazel.info.output_path",
-                "title": "Get Bazel output_path value"
-            },
             {
                 "category": "Bazel",
                 "command": "bazel.lsp.restart",