Templating: Fixes so texts show in picker not the values

[hugohaggmark]

What this PR does / why we need it:
The templating system has gotten less complex when we migrated it to React but there is still at least one big complexity left that still causes us some issues. The complexity I'm talking about is how we for some VariableTypes have support for both single value and multi value. This causes a lot of if statement in our code that tries to handle this and props that can be both string and string[].

This PR does not attempt to solve this complexity, but I think it pushes our code onto a better path. With this PR the current prop will always keep the same type as defined in alignCurrentWithMulti below:

grafana/public/app/features/variables/shared/multiOptions.ts

Line 3 in 1915d10

export const alignCurrentWithMulti = (current: VariableOption, value: boolean): VariableOption => {

This means that OptionsPicker is the only component/class/object/function that transforms the current.text to the correct value which seems a lot clearer to me.

grafana/public/app/features/variables/pickers/OptionsPicker/OptionsPicker.tsx

Line 107 in 1915d10

const getLinkText = (variable: VariableWithOptions) => {

I also did some refactoring of the tests because they weren't using "valid" data.

Which issue(s) this PR fixes:
Fixes #25711
Fixes #25959

Special notes for your reviewer:
There are probably other cases that are messed up with this, but I couldn't find any :)

[torkelo]

Looks good, tested this with an already saved dashboard with many multi-variables and saved in specific multi selection state to make sure there was no problem loading an old dashboard

[hugohaggmark]

Looks good, tested this with an already saved dashboard with many multi-variables and saved in specific multi selection state to make sure there was no problem loading an old dashboard

Thank you @torkelo, before we merge I just want to discuss this change with @mckn because I might miss some of his insights on this.

[mckn]

This looks great! It becomes a lot simpler 🙌

[hugohaggmark]

This looks great! It becomes a lot simpler 🙌

Thank you @mckn

[torkelo]

This caused a very critical bug, causing the All variable not to work (both for normal cases and repeated panels).

#27119

For repeated panels is due to current.text being an array so a comparison with 'All' no longer works:
https://github.com/grafana/grafana/blob/master/public/app/features/dashboard/state/DashboardModel.ts#L654

That explains why repeat no longer works.

Not sure yet why All is not working in a normal query (not rendering to all the values) but probably a similar issue