CDI.setCDIProvider has different behavior than the javadoc states

[manovotn]

CDI.setCDIProvider states that you can only set the provider once but the actual code doesn't check this at all.
Code link - https://github.com/jakartaee/cdi/blob/master/api/src/main/java/jakarta/enterprise/inject/spi/CDI.java#L120

The javadoc makes sense and the code should IMO adhere to it - there is no reason to change CDI provider during runtime.
Since this is behavioral change, we should fix it for next major.

This is also related to #617 since both APIs should work the same way so we should change both.

[Ladicek]

+1 to leaving this to next major. This piece of code is particularly susceptible to Hyrum's law in my opinion :-)