fix(custom text modal): reset practise words on submit (@Quiggleson) (monkeytypegame#6927)

### Description

There was a bug in which the displayed text in the custom text modal was
not being saved when submitted. This occurred when users opened the
custom text modal while taking a test with practice words.

The new behavior is clicking "ok" in the custom text modal calls
`resetBefore()` from `practise-words.ts` to prevent the test from
reverting to the previous list of words.

### Tests
|Action|Behavior|
|---|---|
|Submit some text in the custom text modal without practicing words|The
text in the modal's text area is displayed in the test|
|Submit some text in the custom text modal during a test with practice
words|The text in the modal's text area is displayed in the test|
|set the custom text to practice words twice in a row|The text in the
modal's text area is displayed in the test|
|change the custom text during a test with practice words|The text in
the modal's text area is displayed in the test|


### Checks

- [ ] Adding quotes?
- [ ] Make sure to include translations for the quotes in the
description (or another comment) so we can verify their content.
- [ ] Adding a language?
- Make sure to follow the [languages
documentation](https://github.com/monkeytypegame/monkeytype/blob/master/docs/LANGUAGES.md)
  - [ ] Add language to `packages/schemas/src/languages.ts`
- [ ] Add language to exactly one group in
`frontend/src/ts/constants/languages.ts`
  - [ ] Add language json file to `frontend/static/languages` 
- [ ] Adding a theme?
- Make sure to follow the [themes
documentation](https://github.com/monkeytypegame/monkeytype/blob/master/docs/THEMES.md)
  - [ ] Add theme to `packages/schemas/src/themes.ts`
  - [ ] Add theme to `frontend/src/ts/constants/themes.ts`
  - [ ] Add theme css file to `frontend/static/themes`
- [ ] Add some screenshot of the theme, especially with different test
settings (colorful, flip colors) to your pull request
- [ ] Adding a layout?
- [ ] Make sure to follow the [layouts
documentation](https://github.com/monkeytypegame/monkeytype/blob/master/docs/LAYOUTS.md)
  - [ ] Add layout to `packages/schemas/src/layouts.ts`
  - [ ] Add layout json file to `frontend/static/layouts` 
- [ ] Adding a font?
- Make sure to follow the [themes
documentation](https://github.com/monkeytypegame/monkeytype/blob/master/docs/FONTS.md)
  - [ ] Add font file  to `frontend/static/webfonts`
  - [ ] Add font to `packages/schemas/src/fonts.ts`
  - [ ] Add font to `frontend/src/ts/constants/fonts.ts`
- [ ] Check if any open issues are related to this PR; if so, be sure to
tag them below.
- [x] Make sure the PR title follows the Conventional Commits standard.
(https://www.conventionalcommits.org for more info)
- [x] Make sure to include your GitHub username prefixed with @ inside
parentheses at the end of the PR title.

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Author: Quiggleson

frontend/src/ts/modals/custom-text.ts

@@ -6,6 +6,7 @@ import * as ChallengeController from "../controllers/challenge-controller";
 import Config, * as UpdateConfig from "../config";
 import * as Strings from "../utils/strings";
 import * as WordFilterPopup from "./word-filter";
+import * as PractiseWords from "../test/practise-words";
 import * as Notifications from "../elements/notifications";
 import * as SavedTextsPopup from "./saved-texts";
 import * as SaveCustomTextPopup from "./save-custom-text";
@@ -387,6 +388,7 @@ function apply(): void {
   ChallengeController.clearActive();
   ManualRestart.set();
   if (Config.mode !== "custom") UpdateConfig.setMode("custom");
+  PractiseWords.resetBefore();
   TestLogic.restart();
   hide();
 }