Allow untranslated localization handbacks with English fallback - #127

## Summary
- Use the shared Python localization core and composite action rather
than copying helper scripts into this extension.
- Keep GitHub English submission separate from pull-only DevDiv
stable/pre-release imports.
- Use drop branch dev and canonical extension ID
ms-python.vscode-python-envs; remove tracked generated locale snapshots
where present and keep generated files in VSIX selection.
- Preserve existing runtime metadata, extraction sources, feeds,
platform matrices, and version/validation behavior.
- Require complete, nonempty manifest/runtime tables for all 14
supported locales. Allow untranslated strings and wholly untranslated
tables with English fallback. Reject missing, empty, malformed, or
incomplete handbacks before packaging.

## Shared dependencies
- microsoft/vscode-common-python-lsp#125
-
https://dev.azure.com/devdiv/DevDiv/_git/Pylance-Eng/pullrequest/801431
- Pilot: microsoft/vscode-isort#777

The GitHub action and Azure tooling checkout are pinned to
`6b4a3573e7e7a9fe1e468e129544432278aec2d6`, which implements the
approved English-fallback policy in
microsoft/vscode-common-python-lsp#127. Both
release pipelines use the GitHub-hosted `microsoft/pylance-eng`
templates at `refs/heads/main` through `Github-Pylance`.

## Verification
Executable guards read the actual YAML and preserve existing triggers,
build steps, publication defaults, validation contacts, version flags,
and matrices. Both release YAMLs expanded with publishing explicitly
disabled (environments used the enabled validation definition because
its native definitions are disabled). Actual English export used the
pinned CLI through the internal feed. Changed YAML/JSON formatting and
whitespace checks passed.

## Setup and release prerequisites
The localization drop must contain complete, nonempty manifest/runtime
handbacks for all 14 supported locales; translated content is not a
readiness requirement. Both native DevDiv release definitions remain
disabled; the exact YAML was expanded through the enabled isort
validation definition without enabling them.

Configure the `PYTHON_LOCALIZATION_APP_ID` Actions variable and
`PYTHON_LOCALIZATION_PRIVATE_KEY` secret, or grant access to
organization-level credentials. Credential access was not rechecked for
this feedback update. Configure access through the owners; do not copy
credentials between repositories. Authorize `Github-Pylance` for
template, translation, and shared-tooling repository resources in both
release pipelines.

Merge and publication remain owner-controlled. No merge or publication
is requested.

## GitHub pipeline templates
- Use `microsoft/pylance-eng` on GitHub instead of `DevDiv/Pylance-Eng`
in both stable and pre-release template resources, through the existing
`Github-Pylance` service connection.
- Preserve `refs/heads/main`, template paths, build steps, localization
pins, release settings, and publication defaults. Document
service-connection access for template, translation, and shared-tooling
resources.
- Follow the verified isort change:
microsoft/vscode-isort#793 (test run 15971864
succeeded with publishing disabled and Publish skipped).

### Verification
- Existing executable actual-YAML localization/release guards passed.
- Exact parsed-YAML comparisons against the pre-change commit confirmed
that the template resource is the only release configuration change.
- All fourteen changed sibling release YAMLs passed formatting;
CRLF-aware whitespace checks passed.
- Both native release definitions remain disabled. The exact stable and
pre-release YAMLs expanded successfully through enabled isort definition
27670, covering all 10 configured build platforms. No pipeline was
enabled.
- Expanded pipeline checks preserved localization import ordering,
source scanning, and disabled publishing/validation-stage conditions.

These are preview expansions, not full sibling build runs. No new
release builds were queued, no extension was published, and no PR was
merged.


## Review feedback follow-up
- Runtime environment routing is unchanged from main. Removed the
PR-added routing change, explanatory comments, and added global-refresh
test to keep this PR focused on localization/pipeline work.
- Reconciled the acceptance contract with the README and exact pinned
importer: wholly untranslated tables are allowed with English fallback;
complete/nonempty locale coverage and structural validation remain
required.
- TypeScript compilation, targeted ESLint, whitespace checks, and all 76
focused environment-routing/global-selection tests passed. Verified that
the GitHub action and both release imports use the approved
English-fallback revision.

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Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Copilot-Session: d6166fde-f261-4e66-abe4-3ef5c1313713