Fix GLQL bar chart axis label truncation and date formatting

What does this MR do and why?

GLQL bar charts rendered timestamp dimension labels truncated to 7 characters ("2026...") with the category axis title cramped against the labels. Two defects compound:

1. GlBarChart (GitLab UI) truncates every category (y) axis label to 7 characters and reserves a fixed 64px gutter shared by the labels and the axis title.
2. GLQL passed date-bucket dimension values (2026-01-01, the bucket start from toStartOfInterval) to the chart as raw strings.

This MR:

• Formats date-bucket dimension values as localized dates (Jan 1, 2026 — locale-aware via localeDateFormat, timezone-safe via newDate) at the dimensionValue choke point in app/assets/javascripts/glql/utils/chart_data.js, so bar, column, and line charts, tooltips, and stacked legends all benefit. A round trip through toISODateFormat rejects date-shaped strings that are not real dates (for example 2026-02-30), which Date would otherwise silently roll over to another day.
• Adds barCategoryAxisOptions (app/assets/javascripts/glql/utils/bar_chart_options.js), which sizes the bar chart category (y) axis gutter from the actual labels (~7px per character, clamped to 49–160px) and replaces the 7-character truncation with ECharts pixel-based ellipsis for overly long labels. Both bar chart presenters spread these overrides into their existing option prop, which GlBarChart deep-merges over its defaults.

This works for all date-bucket granularities (daily/weekly/monthly/yearly) because every bucket start is day-aligned. When bucket granularity metadata becomes available to the frontend, dimensionValue is the single place to make the format granularity-aware (for example Jan 2026 for monthly buckets).

Screenshots or screen recordings

All charts query real gitlab.com (gitlab-org/gitlab) data through GLQL analytics mode.

Chart	Before	After
Bar chart, date dimension (monthly buckets)
Bar chart, long string labels (pipeline refs)
Two-dimension bar chart (weekly buckets + status)
Column chart, date dimension
Line chart, date dimension

The column and line charts pick up the date formatting through the shared dimensionValue; their axis geometry is unchanged.

How to set up and validate locally

1. In a project with ClickHouse analytics available, add a GLQL block with a bar chart over a date dimension to any issue or MR description, As an alternative to setting up ClickHouse locally, you can pull !235812 (closed) to route GLQL queries to GitLab.com.

   ```glql
   display: barChart
   mode: analytics
   query: type = Contribution and project = "<group/project>" and created > -6m
   dimensions: created
   metrics: totalCount
   sort: created asc
   ```

2. The y-axis labels render as localized dates ("Jan 1, 2026") instead of "2026...", and the axis title has clearance from the labels.

3. Repeat with display: columnChart and display: lineChart — axis labels and tooltips show formatted dates.

4. Frontend specs: yarn jest spec/frontend/glql.

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