find Phobos dependencies on autodecode

[WalterBright]

trafficstars

To get rid of autodecode, first we must make Phobos independent of whether autodecoding is on or off. So turn it off and see what breaks.

Fixes should be in separate PRs labelled with [no autodecode]. They should be one of:

1. use https://dlang.org/phobos/std_utf.html#byChar
2. use https://dlang.org/phobos/std_utf.html#byDchar
3. hardcode decoding

[dlang-bot]

Thanks for your pull request, @WalterBright!

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Testing this PR locally

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dub fetch digger
dub run digger -- build "master + phobos#7130"

[thewilsonator]

So turn it off and see what breaks.

This should eventually go under a version that we can set defaults on

[WalterBright]

Added [no autodecode] label. Please add this to all PRs that fix autodecoding to work with no autodecoding.