Allow compact maps and sequences for yaml-pro-ts-yank

[taku0]

yaml-pro-ts-yank adjusts indents only if the line is blank.

This commit allows the line to have block struct indicators.

Examples:

Suppose the kill ring have the following fragment:

bbb: 1
ccc: 2

and _ is the point, then:

aaa: _

↓ yaml-pro-ts-yank

aaa: bbb: 1
     ccc: 2

- _

↓ yaml-pro-ts-yank

- bbb: 1
  ccc: 2

? _

↓ yaml-pro-ts-yank

? bbb: 1
  ccc: 2

? aaa
: _

↓ yaml-pro-ts-yank

? aaa
: bbb: 1
  ccc: 2

[zkry]

Thanks for this!