Improve barchart rendering perf by deferring tooltip title creation

[benvinegar]

See #2202

[codecov-io]

Current coverage is 74.78%

Merging #2208 into master will decrease coverage by -0.01% as of cb9e13b

@@            master   #2208   diff @@
======================================
  Files          527     527       
  Stmts        20709   20707     -2
  Branches         0       0       
  Methods          0       0       
======================================
- Hit          15490   15486     -4
  Partial          0       0       
- Missed        5219    5221     +2

Review entire Coverage Diff as of cb9e13b

---

Uncovered Suggestions

1. +0.11% via ...try/utils/apidocs.py#410...432
2. +0.11% via ...try/utils/apidocs.py#117...139
3. +0.10% via ...gs/sentry_helpers.py#182...202
4. See 7 more...

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