refactor: add mnemonics to some gazelle and sphinxdocs actions (bazel-contrib#3449)

Having mnemonics allows actions to be better identified in output, logs,
selected by flags, etc

---------

Co-authored-by: Richard Levasseur <richardlev@gmail.com>

Author: tyler-french

examples/wheel/private/wheel_utils.bzl

@@ -28,6 +28,7 @@ def _directory_writer_impl(ctx):
 
     ctx.actions.run(
         outputs = [output],
+        mnemonic = "PyDirWriter",
         arguments = [args],
         executable = ctx.executable._writer,
     )

gazelle/manifest/defs.bzl

@@ -184,6 +184,7 @@ def _sources_hash_impl(ctx):
     args.add_all(all_srcs)
     ctx.actions.run(
         outputs = [hash_file],
+        mnemonic = "PyGazelleManifestHash",
         inputs = all_srcs,
         arguments = [args],
         executable = ctx.executable._hasher,

gazelle/modules_mapping/def.bzl

@@ -43,6 +43,7 @@ def _modules_mapping_impl(ctx):
 
         ctx.actions.run(
             inputs = [whl],
+            mnemonic = "PyGazelleModMapGen",
             outputs = [wheel_modules_mapping],
             executable = ctx.executable._generator,
             arguments = [args],
@@ -57,6 +58,7 @@ def _modules_mapping_impl(ctx):
 
     ctx.actions.run(
         inputs = per_wheel_outputs,
+        mnemonic = "PyGazelleModMapMerge",
         outputs = [modules_mapping],
         executable = ctx.executable._merger,
         arguments = [merge_args],

sphinxdocs/private/sphinx.bzl

@@ -498,6 +498,7 @@ def _sphinx_inventory_impl(ctx):
     args.add(output)
     ctx.actions.run(
         executable = ctx.executable._builder,
+        mnemonic = "SphinxInventoryBuilder",
         arguments = [args],
         inputs = depset([ctx.file.src]),
         outputs = [output],