DSL's `.startOfLine` should match at start of line.

[milseman]

Currently the DSL's .startOfLine anchor maps to the literal's ^, which is start of input or line depending on options. As proposed it should match at the start of any line. We should probably rename the AST's anchor kind and DSLTree should support a lowered anchor.

rdar://97029630

[milseman]

Similarly for .endOfLine.