Tables: Freeze with regex-formatted variables

### What happened? See reproducing. ### What did you expect to happen? The variable rendered like it is in the docs play site (https://grafana.com/docs/grafana/latest/dashboards/variables/variable-syntax/#advanced-variable-format-options), text field. ### Did this work before? No ### How do we reproduce it? 1. Create custom variable, where value has dot in it (`hello.`) 2. Use it anywhere in table with `${foo:regex}`, for example in a table column name or a filter. 3. Table stuck loading. When saved, table can't be edited, `An unexpected error: bad escaped character at line 1 column 120 of the JSON data` ### Is the bug inside a dashboard panel? | Key | Value | |--|--| | Panel | table @ 12.1.0 | | Grafana | Grafana v12.1.0 (ccd7b6ce7e) // Open Source | <details><summary>Panel debug snapshot dashboard</summary> ```json { "panels": [ { "id": 2, "type": "table", "title": "Reproduced with embedded data", "gridPos": { "h": 13, "w": 15, "x": 0, "y": 0 }, "fieldConfig": { "defaults": { "custom": { "align": "auto", "cellOptions": { "type": "auto" }, "inspect": false }, "mappings": [], "thresholds": { "mode": "absolute", "steps": [ { "color": "green", "value": null }, { "color": "red", "value": 80 } ] }, "color": { "mode": "thresholds" } }, "overrides": [] }, "transformations": [ { "id": "organize", "options": { "excludeByName": {}, "includeByName": {}, "indexByName": {}, "renameByName": { "mediaType": "${va:regex}a", "size": "" } } } ]…