Validate mnemonic words in MnemonicGrid

[lukaw3d]

Quick improvement since #1181 disables spell-checking mnemonic

Before 1181	After 1181 + this

[github-actions]

🦙 MegaLinter status: ✅ SUCCESS

Descriptor	Linter	Files	Fixed	Errors	Elapsed time
✅ EDITORCONFIG	editorconfig-checker	4		0	0.01s
✅ REPOSITORY	checkov	yes		no	12.23s
✅ REPOSITORY	git_diff	yes		no	0.0s
✅ TSX	eslint	2	0	0	3.66s

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[pro-wh]

oh good, this might help people who used a wrong word that's coincidentally a real word

did we support importing mnemonics from other languages? if so, those users will have to ignore this

[lukaw3d]

🎉 we didn't support other languages; and bip39 now discourages them https://github.com/bitcoin/bips/blob/master/bip-0039.mediawiki#wordlists

Fun fact: Japanese mnemonics don't use a normal space, so even our word splitting wouldn't work

[codecov]

Codecov Report

Merging #1180 (8092d0e) into master (cf54100) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1180      +/-   ##
==========================================
- Coverage   81.05%   81.04%   -0.01%     
==========================================
  Files         140      140              
  Lines        2639     2638       -1     
  Branches      648      646       -2     
==========================================
- Hits         2139     2138       -1     
  Misses        500      500              

Flag	Coverage Δ
cypress	51.50% <100.00%> (-0.02%)	⬇️
jest	74.24% <100.00%> (-0.01%)	⬇️

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Impacted Files	Coverage Δ
src/app/components/MnemonicGrid/index.tsx	100.00% <100.00%> (ø)