RFC: Simplify SyntaxContext and Mark

[kdy1]

We don't use complex features of SyntaxContext nor Mark.

For @swc/core and next-swc, we only need

• Parent-child relationship for Mark
• SyntaxContext.apply_mark()

But I want to know if there's a project using more complex features.

[g-plane]

What're complex features?

[kdy1]

• Mark#set_is_builtin && Mark#is_builtin (https://rustdoc.swc.rs/swc_common/struct.Mark.html#method.is_builtin)
• SyntaxContext#*_adjust (https://rustdoc.swc.rs/swc_common/struct.SyntaxContext.html)

[swc-bot]

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