collapse consecutive whitespace characters

[Rich-Harris]

Sort of a last-minute thing but the prevalence of strings like "\n\n\t\t\t" in the generated code is a frequent complaint. This PR introduces a preserveWhitespace compiler option — if it's not true, and a given text node isn't inside a <pre>, those strings will be replaced with space().

There are almost certainly other things we can do to reduce the need even for these — #189 — but this seems like an obvious starting point.

[codecov-io]

Codecov Report

Merging #2258 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2258   +/-   ##
=======================================
  Coverage   91.83%   91.83%           
=======================================
  Files           1        1           
  Lines          49       49           
=======================================
  Hits           45       45           
  Misses          4        4

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[Rich-Harris]

no-one has freaked out about this so i'm going to merge it in

[Ryuno-Ki]

I recall that there are some CSS properties controlling whitespace behaviour as well...

But I guess, people will notice and fill tickets then.