all: add break & continue loop actions

[jo3-l]

Description
This implements break and continue actions for range and while loops, along with tests. It's mostly taken from https://go-review.googlesource.com/c/go/+/66410/ with some edits to support while actions. The above commit was reverted due to issues with html/template (see golang/go#23683). However, as we don't have such issues, there should be no issue adding it to this fork.

There is also a newer CL that implements it upstream (not merged); see the comment below for why that approach is not used here.

Status
Tests are all passing except the newline ones mentioned earlier, which are unrelated to this PR.

[jo3-l]

Re-drafting this as https://go-review.googlesource.com/c/go/+/321491/1/src/text/template/exec.go - a new CL implementing break/continue upstream - uses a different, far simpler approach than the original PR this was inspired by, which I'd like to change this PR to use as well.
Had to roll back these changes after trying a similar technique with the return/execTemplate PR, which caused a ~50x performance regression in self-calling associated templates. This will still use the old approach for that reason.

[ashishjh-bst]

Has conflicts after the try catch and while features have been merged @jo3-l

[jo3-l]

Rebased.

[ashishjh-bst]

@jo3-l has conflicts again after merging your Other PR, I'll merge this one and then use the version after merging this PR for monorepo.

[jo3-l]

The other PR is a superset of this one (it builds on this) so since that's merged there's no need for this one. Closing.

[mrbentarikau]

just interested, what Other PR, thnx...
is it #6?

[jo3-l]

Yes, I was referring to #6 in my previous message.