Snippets update: add more snippets and change their naming convention

[EmilyGraceSeville7cf]

• document all snippets via documentation
• add snippets for commands like if with [[ command
• add more sed and awk snippets
• change naming convention to make labels more descriptive (but longer)
• add snippet for function doc (closes Add snippet for documenting functions (I will implement) #781)
• snippets for jq, yq

[EmilyGraceSeville7cf]

@skovhus, what to do with these failures?

[Shane-XB-Qian]

@EmilySeville7cfg
those if-else.test and while.test was verified and worked at your side?

[EmilyGraceSeville7cf]

@Shane-XB-Qian, yep. ;) I've checked them.

[Shane-XB-Qian]

@EmilySeville7cfg
would you mind change those - and . delimiters in if-else.test (uniformed) to _, e.g 'if_else_test` ?

or at least Not use . in its label.

maybe that's not a problem in vscode, but in vim, normally - and . was not a keyword char, but maybe a trigger char.
maybe i can make that - work at my side, though buggy still.

[EmilyGraceSeville7cf]

would you mind change those - and . delimiters in if-else.test (uniformed) to _, e.g 'if_else_test` ?

I can change it to - for now. Hoply send PR today or tomorrow to fix this issue. Didn't know about such problem with Vim.