Check for translation missing accelerator keys

[softins]

Short description of changes

Adds a check to tools/checkkeys.pl to display a warning if an original English string contains an &accelerator key and the corresponding translation does not.

CHANGELOG: Tools: Updated checkkeys.pl to flag missing accelerator key in translation.

Context: Fixes an issue?

Just a useful check I thought of when reviewing #3620 and noticed a translation had not included an accelerator key, when there was one in the English original. This is the output for the current tree of that PR:

Language: de_DE
Language: es_ES
Language: fr_FR
Language: it_IT
Language: ja_JP
Language: ko_KR
Language: nb_NO
Language: nl_NL
Language: pl_PL

*** TRANSLATION MISSING ACCELERATOR KEY ***
Original: Clear &All Stored Solo and Mute Settings
Translation: Wyczyść wszystkie ustawienia solo/wycissz

Language: pt_BR
Language: pt_PT
Language: ru_RU
Language: sk_SK
Language: sv_SE

*** TRANSLATION MISSING ACCELERATOR KEY ***
Original: Sort Users by Chann&el
Translation: Sortera användare efter kanal

*** TRANSLATION MISSING ACCELERATOR KEY ***
Original: P&rivacy policy...
Translation: Integritetspolicy...

Language: th
Language: zh_CN
......

So it flagged up a couple of other existing translations, in addition to the new one I noticed initially.

Does this change need documentation? What needs to be documented and how?

Not really.

Status of this Pull Request

Ready

What is missing until this pull request can be merged?

Just review.

Checklist

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