Disable trimming of metatag separator [#3490986]

Problem/Motivation

The metatag separator is being trimmed, which reduces the possibility of having a separator followed by a space.
For example: You can't have "Value1, Value2", but only "Value1,Value2" or "Value1 | Value2", but only "Value1|Value2".

Steps to reproduce

1. Go to /admin/config/search/metatag/settings.
2. Set the separator value to " | ".
3. Save the form.
Result: The separator value is trimmed.

Proposed resolution

Remove the trimming behavior. Set the user's responsibility to remove any unnecessary spaces.

Issue fork metatag-3490986

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3490986-disable-trimming-of changes, plain diff MR !164
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