Split ChapelBase out into logical modules

[ronawho]

ChapelBase is a grab bag/hodgepodge of misc support functions, classes, and other stuff.

We should split it up into logical modules for maintainability/organization as well as documentability reasons.

It includes things such as:

• config variable helper routines
• compilerError, compilerWarning, compilerAssert
• iterKind enum
• assignment, equality (==, !=) , relational operations, unary/binary ops, bitwise ops, and op= support
• _statementLevelSymbol support
• _cond_test support
• complex support
• min/max
• exit support
• _ddata support
• casts
• _EndCount support
• various auto/init copys
• some first-class-function support?
• is*Type? support
• QIO externs
• _defaultOf's
• and probably some other stuff

[ronawho]

As noted in #4627 compilerError, compilerWarning, and compilerAssert should be split into their own module, which should help us get rid of the lame UtilMisc_forDocs.chpl module

[e-kayrakli]

A related effort could be to sift through StringCasts and BytesCasts and move casts to the relevant types' modules if such a thing exist, and think about what to do with more primitive types' casts like int:string.