ament: install .srv and .action definitions alongside .msg files

[xiangguomin]

Summary

Fixes #626.

The IDL source loop in _create_ament_setup (ament.bzl) had an early-exit guard that silently dropped .srv and .action files from the ament share tree:

# Before
for src in idl.srcs:
    if src.extension != "msg":
        continue   # .srv and .action files never installed
    src_file = ctx.actions.declare_file(
        paths.join(prefix_path, "share", package_name, "msg", src.basename),
    )
    ...
    idl_manifest_contents.append(paths.join("msg", src.basename))

Any runtime type-introspection tool (foxglove_bridge, ros2 service call, ros2 interface show) that looks for definitions at share/<pkg>/srv/ or share/<pkg>/action/ would not find them and fall back to IDL, producing warnings like:

[WARN] no .msg definition for rcl_interfaces/srv/DescribeParameters_Request, falling back to IDL
[WARN] Could not find definition for type rcl_interfaces/srv/DescribeParameters: rcl_interfaces/srv/DescribeParameters_Request

Fix

Route each source into its matching subdirectory (msg/, srv/, action/) under share/<pkg>/ instead of hardcoding msg/ for all types:

# After
for src in idl.srcs:
    if src.extension not in ("msg", "srv", "action"):
        continue
    subdir = src.extension
    src_file = ctx.actions.declare_file(
        paths.join(prefix_path, "share", package_name, subdir, src.basename),
    )
    ...
    idl_manifest_contents.append(paths.join(subdir, src.basename))

Test

Verified by building a ros2_cpp_binary with idl_deps = ["@ros2_rcl_interfaces//:rcl_interfaces"] and confirming that share/rcl_interfaces/srv/DescribeParameters.srv (and all other .srv files) are present in the ament_setup output tree. The foxglove_bridge "Could not find definition" warnings are gone after this change.