REF: move more methods to EAMixins
With the exception of the comparison ops, this is the last stuff that can be moved before I have to implement the constructors (and hence a buttload of tests).  Let's get this out of the way first.

(For the comparison ops there is some super jujitsu that needs to be un-wound, so will do that separately)
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21782?src=pr&el=h1) Report
> Merging [#21782](https://codecov.io/gh/pandas-dev/pandas/pull/21782?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/620abc403d371446afe38fc1e63f0d90ea27b80a?src=pr&el=desc) will **increase** coverage by `<.01%`.
> The diff coverage is `95%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/21782/graphs/tree.svg?src=pr&token=eZ4WkYLtcO&width=650&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/21782?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #21782      +/-   ##
==========================================
+ Coverage   91.95%   91.95%   +<.01%     
==========================================
  Files         160      160              
  Lines       49820    49840      +20     
==========================================
+ Hits        45812    45832      +20     
  Misses       4008     4008
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.33% <95%> (ø)` | :arrow_up: |
| #single | `42.08% <45%> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/21782?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/indexes/datetimes.py](https://codecov.io/gh/pandas-dev/pandas/pull/21782/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9kYXRldGltZXMucHk=) | `95.23% <ø> (-0.06%)` | :arrow_down: |
| [pandas/core/indexes/datetimelike.py](https://codecov.io/gh/pandas-dev/pandas/pull/21782/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9kYXRldGltZWxpa2UucHk=) | `96.97% <ø> (-0.02%)` | :arrow_down: |
| [pandas/core/arrays/datetimelike.py](https://codecov.io/gh/pandas-dev/pandas/pull/21782/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYXJyYXlzL2RhdGV0aW1lbGlrZS5weQ==) | `94.62% <100%> (+0.24%)` | :arrow_up: |
| [pandas/core/indexes/period.py](https://codecov.io/gh/pandas-dev/pandas/pull/21782/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9wZXJpb2QucHk=) | `93.58% <100%> (+0.22%)` | :arrow_up: |
| [pandas/core/indexes/timedeltas.py](https://codecov.io/gh/pandas-dev/pandas/pull/21782/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy90aW1lZGVsdGFzLnB5) | `91.02% <100%> (+0.02%)` | :arrow_up: |
| [pandas/core/arrays/datetimes.py](https://codecov.io/gh/pandas-dev/pandas/pull/21782/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYXJyYXlzL2RhdGV0aW1lcy5weQ==) | `100% <100%> (ø)` | :arrow_up: |
| [pandas/core/arrays/period.py](https://codecov.io/gh/pandas-dev/pandas/pull/21782/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYXJyYXlzL3BlcmlvZC5weQ==) | `89.77% <84.61%> (-0.9%)` | :arrow_down: |
| [pandas/core/arrays/timedelta.py](https://codecov.io/gh/pandas-dev/pandas/pull/21782/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYXJyYXlzL3RpbWVkZWx0YS5weQ==) | `98.27% <96%> (-1.73%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21782?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/21782?src=pr&el=footer). Last update [620abc4...10e5559](https://codecov.io/gh/pandas-dev/pandas/pull/21782?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
