EnzoInitialShuCollapse parameter refactorization

[jakereinheimer]

Pull request summary

Refactoring EnzoInitialShuCollapse parameters. Addresses issue #383. Short because I am going through it live with Matthew

[jwise77]

There are some compilation errors

/home/circleci/enzo-e/src/Enzo/initial/EnzoInitialShuCollapse.cpp:21:4: error: expected ‘{’ before ‘center_’
   21 |    center_{}
      |    ^~~~~~~
/home/circleci/enzo-e/src/Enzo/initial/EnzoInitialShuCollapse.cpp: At global scope:
/home/circleci/enzo-e/src/Enzo/initial/EnzoInitialShuCollapse.cpp:21:4: error: ‘center_’ does not name a type
/home/circleci/enzo-e/src/Enzo/initial/EnzoInitialShuCollapse.cpp:22:4: error: ‘drift_velocity_’ does not name a type
   22 |    drift_velocity_{}
      |    ^~~~~~~~~~~~~~~
/home/circleci/enzo-e/src/Enzo/initial/EnzoInitialShuCollapse.cpp:23:1: error: expected unqualified-id before ‘{’ token
   23 | {
      | ^

[mabruzzo]

This is fantastic! I really appreciate you doing this!

I highlighted 2 missing commas that are needed in order to get this to compile properly.

There are also 2 other changes that are necessary:

1. The order in which the members appear in the "member-initializer-list" in the constructors should match the order in which they are declared within the class itself (jump to the end of EnzoInitialShuCollapse to see this ordering).
   • technically, this is not strictly necessary, but it's good practice (if you don't do this, you can get unexpected behavior while using one member to initialize another member)
   • plus g++ raises some annoying warnings if you don't do this
2. More importantly, you are changing the default value of the parameters
   • this is my fault for not explaining this.
   • When you call something like p.value_float("truncation_radius", ...) the trailing value represents the default value.
   • Currently, you've changed the default values compared to what was previously used within EnzoConfig::read_initial_shu_collapse_