Partial search with keywords not working

It was reported in 3709820-zen that if we search using partial keywords in numeric characters that don't contain the initial characters on the line, the search result will not show the notes that contain the search term.

For example, a note with the number 123456 will not show up in the search result if we search using 456. The result shows up only if we search using the exact number - 123456 or 123.

### Expected

I would expect to be able to search for the notes even with partial keywords that contain numeric characters.

### Observed

I can only search for the note with the exact numbers or a keyword that contains the first few characters on the line.

### Reproduced

1. Create a note with the numbers `5558890 123456`
2. Search using the keyword `123` or `123456`
3. No search result found
4. Search using the keyword `555` or `555 123`
5. Search result found for the note created in Step 1

**Replicated on**

Device Make: OPPO
Device Model: Reno 4
Android Version: 10
Simplenote Version: 2.16-rc-3 (133)

I wonder if this is an enhancement mentioned [here](https://github.com/Automattic/simplenote-android/issues/873).

Start by reproducing the numbered search steps in the Android app with a note containing "5558890 123456", then trace the search entry point and matching logic. The issue names no files or tests, so locate the relevant search implementation first; done means partial numeric terms such as 123 return the note while existing exact and prefix searches still work.

Written by the indexing model from the issue text.