Update TS to 7

[richard-cox]

• We're on TS 5
• There are HUGE performance improvements in TS 7, we should update
• We should compare TS errors before upgrade and after to ensure we don't regress
  • Add type check script #18226 covers the current list, and will breadcrumb to issues that fix them
• Some TS deps will also need bumping / TLC
  • ts-jest[versions] (WARN) Version 5.6.3 of typescript installed has not been tested with ts-jest. If you're experiencing issues, consider using a supported version (>=3.8.0 <5.0.0-0). Please do not report issues in ts-jest if you are using unsupported versions.

[richard-cox]

Blocked on #18157 (and 2.15 branch)