Write the module's own prose in American English

Closes [#3624521].

80 British spellings in 47 files, swept to American: cancelling x53, honour/honoured/honours x19, modelled/modelling x6, favour x2.

Nineteen were on the documented API surface - OrchestraClientInterface::start() and WireAccount both described a name being honoured - and six were in pages the documentation site publishes. One was a string a person reads, the instance listing's batch title, so its French entry moved with it and scripts/check-translations.php still reports 38 of 38 catalogs.

The diff is 79 changed lines carrying those 80 occurrences (one line holds two): comments and docblocks, three lines of published documentation, two assertion messages, and the one t() string above. Nothing else changes.

No guard comes with it

An earlier version of this MR moved the page-scoped spelling rule in DocumentedSurfaceTest into HouseVocabularyTest and widened it to every class. Both of those classes are gone as of [#3624520], along with the rest of the tests that read source files to assert things about the words in them. Tests are for code logic; a spelling problem gets fixed in the spelling.

So this is a prose fix and nothing more. cspell stays the lint lane for spelling, and it is green either way on these four words - its en-US dictionary accepts both forms, which is why they accumulated.

Rebased onto 1.x after [#3624518], [#3624519] and [#3624520] merged. The two commits that touched DocumentedSurfaceTest and HouseVocabularyTest dropped out in the rebase, since 1.x deletes both files.