[lexical-playground] CI: standardise key press delay

[potatowagon]

Description

credits to @Sahejkm for pointing out that 100ms is workable as a delay https://github.com/facebook/lexical/pull/6245/files#r1625266582

introducing const STANDARD_KEYPRESS_DELAY_MS

• setting 100ms as a standard keypress delay const, so it can be reused and developers dont need to waste time through trial an error to find an optimal delay value
• the goal of this standard delay is to provide a delay value that is short enough yet not too short such that keypresses still override each other thus leading to flakiness
• this standard should work for most test cases. if there are outliers, a custom value can be passed as the delay instead
• open to adjusting this standard value overtime

Closes #

Test plan

npm run start & npm run test-e2e-collab-chromium

  Slow test file: [chromium] › packages/lexical-playground/__tests__/e2e/Mentions.spec.mjs (19.9s)
  Consider splitting slow test files to speed up parallel execution
  1 flaky
    [chromium] › packages/lexical-playground/__tests__/e2e/Tables.spec.mjs:1269:3 › Tables › Grid selection: can select multiple cells and insert an image 
  66 skipped
  370 passed (3.9m)

tests using the 100ms delay not in flaky list

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Name	Status	Preview	Comments	Updated (UTC)
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[github-actions]

size-limit report 📦

Path	Size
lexical - cjs	28.33 KB (0%)
lexical - esm	28.14 KB (0%)
@lexical/rich-text - cjs	36.77 KB (0%)
@lexical/rich-text - esm	28.1 KB (0%)
@lexical/plain-text - cjs	35.35 KB (0%)
@lexical/plain-text - esm	25.33 KB (0%)
@lexical/react - cjs	38.51 KB (0%)
@lexical/react - esm	29.12 KB (0%)