Avoid modifying Compile_dex property

Previously, the code would modify the Compile_dex property to set it to
true if the module was part of an APEX as the APEX needs the dex file.
That lost information about whether the Compile_dex property was
specified in the .bp file and also meant that the APEX variant had
different properties to other variants which could result in unexpected
differences in behavior between them.

One of those differences can occur in the sdk snapshot generation code
which uses the Compile_dex property to determined whether to write a
compile_dex property in the generated snapshot. If it uses an APEX
variant then it will always add compile_dex: true but if it used a non
APEX variant then it would depend on the setting of compile_dex in the
source. That leads to the generated snapshot being affected not just
by the set of modules that are included but also how they were
specified.

This change stops modifying the properties and just uses a local
variable to store the updated value. All the other (4) uses of the
Compile_dex property were checked and 1 accesses the property before
it is updated, 2 access the property from a module type (Import) that
does not update the property and the other is in the sdk snapshot
generation code which accesses it after it has been modified but needs
to access the unmodified value.

This is needed for the follow up change that allows an sdk module to
reference an apex to automatically add exportable parts of the apex
contents to the sdk snapshot avoiding duplication which can lead to
errors.

Bug: 232401814
Test: m nothing
Change-Id: Ibc80d93473a266dc9f9900ec1cb175b51460b5e9