Block args set by fields are static and never change. Inputs that do
change are always set onto args. With these two assumptions we can
reuse the same objects for each execution of the same block instead of
constantly creating them and letting them be garbage collected.
Use a private StackFrame class to help internally manage use of Stack
Frame values and memory. Create params, reported, and executionContext
on demand.
Explain how BlocksExecuteCache helps speed up execute by storing values from
Blocks and one-time derived values on an object that is released when Blocks is
edited in the editor. The one time created cache object for a block then
simplifies the complexity of later javascript operations to use these stored
values.
The new `maybeFormatMessage` function detects whether its argument
looks like a message descriptor object and, if so, will call
`formatMessage` on it. This is now used for all user-visible text fields
in extensions.
Also, messages may use "select" to check the target type with a message
like this: '{targetType, select, stage {text for stage} sprite {text for
sprite} other {text for other}'. Note that the "other" clause is
required by `formatMessage`.
A LOOP block is like a conditional, but the LOOP block will be
re-evaluated after any child branch runs.
Also:
- Support using '---' as a block separator
- Refactor common code from `_registerExtensionPrimitives` and
`_refreshExtensionPrimitives` into new `_fillExtensionCategory`
- Improve error reporting during block conversion
This involves adding a new opcode, event_whenstageclicked, and adding a
method to the blocks container to update the opcode pair depending on
whether the target is the stage. This method is then called in two
places: first after the sb2 import parses the blocks (not done in the
sb2 parsing itself because no other blocks are target specific) and then
again when blocks are shared between targets.
Also added tests for the block container method, and a fixture project
that tests the opcode splitting on sb2 import.
The previous logic seemed to be expecting `peekStack` to return 0 when
the stack was empty, but its return type is `?string` and it returns
`undefined` when the stack is empty. The `!== 0` check would never pass,
then, leading to problems with (for example) the "say/think and wait"
blocks.
