Adds Conditional Compilation Statements to the AST

[markwpearce]

Conditional compile directives (#if, #const, #error, etc.) are now part of the AST, and as such, the branches of the condition compiles can be walked.

There is one concession with this: #if blocks are treated as any other block, and everything in them must be self contained, or will cause a diagnostic.

That means that even though this is allowed in Brightscript:

sub foo()
# if true
end sub
#end if

it will cause some diagnostics, because the sub foo() is partially inside and outside the #if statement

• [x] TODO - Add some walk mode options that allow walking the tree based on true/false const values.

• [x] Support #if not <bs_const> #1158

Addresses #1023

[markwpearce]

I suppose we should support #if not <bs_const> as well? #1158

[TwitchBronBron]

I suppose we should support #if not <bs_const> as well? #1158

Yes, if we can!