Moving the support code in a easier to use place

[Iximiel]

Description

@gtribello
as we discussed I am moving the code into easier-to-use places
I am doing a commit per piece of code, starting from the View.

The plan is

• View
• View2D
• MultiColvarInput
• ColvarInput
• ColvarOutput

right?
Colvar input and ouput will likely end up in the same file

I will set up the PR directly with the versions of those classes that works for openacc, to simplify the rebasing/merging of #1206

For the changes in Pbc, as now I am using using to speed up, but in a second moment we can change "memoryView" to plain view

Target release

I would like my code to appear in release XXXXX

Type of contribution

• changes to code or doc authored by PLUMED developers, or additions of code in the core or within the default modules
• changes to a module not authored by you
• new module contribution or edit of a module authored by you

Copyright

• I agree to transfer the copyright of the code I have written to the PLUMED developers or to the author of the code I am modifying.

• the module I added or modified contains a COPYRIGHT file with the correct license information. Code should be released under an open source license. I also used the command cd src && ./header.sh mymodulename in order to make sure the headers of the module are correct.

Tests

• I added a new regtest or modified an existing regtest to validate my changes.
• I verified that all regtests are passed successfully on GitHub Actions.

[gtribello]

HI @Iximiel

I think that the following tools can be moved to the tools directory:

• View
• View2D
• ColvarOutput

MultiColvarInput will likely only be ever used in MultiColvarTemplate. If you want to move it to a separate file in the colvar module that is fine with me. However, if it were me, I would just leave those definitions in MultiColvarTemplate.

Similarly, ColvarInput is likely only going to be used in files that include MutiColvarTemplate. I would thus also be tempted to leave these definitions in MultiColvarTemplate. It could also be put in a separate file in the colvar module, though.

[Iximiel]

My intention was to put those in this PR, sorry for the misunderstaning.

And I was sure to have opened this as a draft to block the merge until done...

I will open a new PR with all the changes