fix Issue 13847 - CTFE internal error: dottype

Handle function values in each CTFE steps, then simplify
CallExp::interpret() and we need to interpret CallExp::e1 just only once.

After all, DotTypeExp will be one of the function values in CTFE, and
CallExp::interpret can distinguish 'virtual call' and 'direct call' properly.

Also simplify ThisExp::interpret because pthis is always interpreted to a
literal expression (TOKstructliteral or TOKclassreference).
fix Issue 13028 - [ICE] CTFE internal error: cannot evaluate at compile time
fix Issue 13528 - Internal Compiler Error: CTFE DotType
Merge pull request #4208 from 9rnsr/fix13847

Issue 13847 - CTFE internal error: dottype
fix Issue 13832 - delegates that return ref do not output correctly to .di file
Merge pull request #4201 from 9rnsr/fix13832

Issue 13832 - delegates that return ref do not output correctly to di file
fix Issue 13784 - Wrong code with modulo operation and optimisations enabled
Merge pull request #4214 from WalterBright/fix13784

fix Issue 13784 - Wrong code with modulo operation and optimisations ena...
fix Issue 13864 - tuple expand causes range violation
Merge pull request #4216 from 9rnsr/fix13864

[REG2.066] Issue 13864 - tuple expand causes range violation
fix 13776 - Incorrect "recursive alias declaration" error with `__traits(compiles, ...)`
Change remaining old 'offset' deprecation to error
fix Issue 12776 - Wrong type for __vector(int[4]).init
fix Issue 12163 - pdb debugging (win64): stepping loops points to incorrect lines
Merge pull request #4217 from 9rnsr/fix12776

Issue 12776 - Wrong type for __vector(int[4]).init
Merge pull request #4219 from WalterBright/fix12163

fix Issue 12163 - pdb debugging (win64): stepping loops points to incorr...
Merge pull request #4172 from 9rnsr/fix13776

[REG2.067a] 13776 - Incorrect "recursive alias declaration" error with `__traits(compiles, ...)`
Add manually ported frontend source files to version control
Add settings file and makefile targets to build ddmd
Add generated source to .gitignore