without a Python dependency

Gbp-Dch: Full

Closes: #736229
Closes: #781096
Closes: #856950
Closes: #953676
Closes: #1085107
Closes: #1085602

Closes: #1072541

Update to upstream version '48.1'
with Debian dir 790054f8356a2e640571baa3240bb1011c35add2

This also changes the api_version to 48.1 since there are some
incompatibilities.

It will also be removed from the libgedits.

The rationale: I don't see the usefulness of this feature. If it is to
better see indentation levels, follow the Linux kernel guideline to
indent with real tabs (8 chars length), that way the indentation levels
are clear enough.

My gut feeling is that there are better ways to solve the problem(s)
that this feature was trying to fix.

Note: in gedit the feature was added in 2015 with
commit 62f654dc

The warning was:

Gedit: invalid "closure" annotation: only valid on callback parameters

But the function isn't used in Python plugins from gedit-plugins.