pygmt.x2sys_cross: Deprecate parameter runtimes to run_times (Will be removed in v0.20.0)

[yvonnefroehlich]

Description of proposed changes

Use underscores between words in parameter names; related to #2014.

Preview: https://pygmt-dev--4294.org.readthedocs.build/en/4294/api/generated/pygmt.x2sys_cross.html

Guidelines

• General Guidelines for Pull Request
• Guidelines for Contributing Documentation
• Guidelines for Contributing Code

Slash Commands

You can write slash commands (/command) in the first line of a comment to perform
specific operations. Supported slash command is:

• /format: automatically format and lint the code

[seisman]

I think runtime is a single word in computer science (https://en.wikipedia.org/wiki/Execution_(computing)#Runtime).

[yvonnefroehlich]

I think runtime is a single word in computer science (https://en.wikipedia.org/wiki/Execution_(computing)#Runtime).

I was also wondering if this could be considered as one word. Fine with keeping this parameter without an underscore. Closing this PR.