PG-1437 Clean up frontend and backend sources in meson.build

[jeltz]

There is no reason why we cannot just concatenate the two lists. And while at it we also sort and reindent the lists.

While the frontend sources right now are a strict subset of the backend
sources that might not always be the case so keep them as separate lists
but clean them up. In the long term we want to refactor this entirely
anyway so let's not overcomplicate this.

[AndersAstrand]

I might have missed some previous discussion, but are we sure that adding an assumption that the frontend code is a subset of the extension code is what we want to do?

I'm thinking it might compound the possible confusion by #ifdef FRONTEND sprinkled throughout the code rather than help.

The old naming leads me to believe the list of files for "decrypt" arent necessarily frontend files but files used by both the extension and the frontend?

So I'd suggest either separate lists of files for frontend and extension, or if we want to group the files needed for decryption separately have both the frontend and extension file list concatenate it.

[jeltz]

Good point, need to think about it. But calling them decrypt isn't entirely accurate either because those files are for the following:

• Reading and writing to the keyring file
• Reading the key file (require connecting to key server)
• Reading encrypted WAL (requires connecting to key server)

But it does not include for example:

• Reading encrypted relations

[jeltz]

Kept them as separate.