TYPO: IntervalIndex.symmetric_differnce -> IntervalIndex.symmetric_difference
- [X] closes #18475
- [X] tests added / passed
- [X] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [X] whatsnew entry

Before this, `IntervalIndex.symmetric_difference` hit the base class implementation, and appeared to generally be working, albeit without full error handling and with worse performance than the intended implementation.

Also went through and did some more work on the tests:

- expanded the `test_set_operation_errors`, since this didn't have full coverage of all set ops prior.
- `self.create_index` previous only created an index with two elements, which seemed kind of small; increased this to 10 elements, and updated impacted tests accordingly.
- added a fixture for parameterizing over `name`, and updated a few tests to use this.
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18476?src=pr&el=h1) Report
> Merging [#18476](https://codecov.io/gh/pandas-dev/pandas/pull/18476?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/38f41e64f4b8a0479f8835022af5e7343ccf8498?src=pr&el=desc) will **increase** coverage by `0.01%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/18476/graphs/tree.svg?height=150&width=650&token=eZ4WkYLtcO&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/18476?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #18476      +/-   ##
==========================================
+ Coverage    91.3%   91.31%   +0.01%     
==========================================
  Files         163      163              
  Lines       49781    49781              
==========================================
+ Hits        45451    45456       +5     
+ Misses       4330     4325       -5
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.11% <100%> (+0.01%)` | :arrow_up: |
| #single | `40.72% <100%> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/18476?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/indexes/interval.py](https://codecov.io/gh/pandas-dev/pandas/pull/18476?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9pbnRlcnZhbC5weQ==) | `93.56% <100%> (+0.86%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18476?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18476?src=pr&el=footer). Last update [38f41e6...9f6411b](https://codecov.io/gh/pandas-dev/pandas/pull/18476?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 thanks @jschendel 