Path validation fix, webpack process polyfill, and v9 DataGrid column resize UX

[rafarhat]

This PR bundles several independent fixes and enhancements.

1. Path validation: allow valid IoT Hub device ID characters

The validatePath regex was too restrictive, blocking dots and other special characters that are valid in IoT Hub device IDs per Azure documentation (- . % _ * ? ! ( ) , : = @ $ '). This caused "Invalid path: contains disallowed characters" errors for device IDs like test.test2. Path traversal (..) and double slashes (//) are still blocked.

2. Webpack: provide process polyfill in the common config

Moved the process ProvidePlugin from the dev-only webpack config into the shared webpack.common.ts so the production (electron file://) bundle also has the polyfill. Fixes a "process is not defined" runtime error that only reproduced in the production build.

3. Restore v8-style column resize UX in the v9 DataGrid wrapper

The app was migrated from Fluent UI v8 (DetailsList) to v9 (DataGrid); the shared ResizableDetailsList lost the v8 resize experience. This restores it:

• Working resize via className-based cell styling, fixing a v9 gotcha where consumer inline style clobbered the column-sizing width that DataGridHeaderCell/DataGridCell inject.
• Header dropdown menu per column with a "Resize Column" dialog for exact-pixel width entry, plus a keyboard-resize option.
• Chevron indicator on each header to signal the menu.
• Horizontal scroll wrapper (.rdl-scroll-container) so the grid shows a horizontal scrollbar when the window is narrower than the columns'' combined minimum widths — matching v8 DetailsList behavior.
• Accessibility: header cells use the visible column name as their accessible name (no static aria-label override); the menu trigger still announces aria-haspopup.

4. Cleanup

Removed an accidentally committed generated file (host/handlers/urlValidation).

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