Increase performance in Liquid::Lexer#tokenize

[Watson1978]

To obtain String Literal, the regular expression might be executed at two times.
It would be slightly faster to run them all at once using Regexp.union.

−	before	after	result
parse	63.418	65.183	1.028x
render	195.389	195.648	-
parse & render	46.091	46.917	1.018x

Environment

• MacBook Pro (14 inch, 2021)
• macOS 13.0 Beta
• Apple M1 Max
• Ruby 3.1.2

Before

Running benchmark for 10 seconds (with 5 seconds warmup).

Warming up --------------------------------------
              parse:     6.000  i/100ms
             render:    19.000  i/100ms
     parse & render:     4.000  i/100ms
Calculating -------------------------------------
              parse:     63.418  (± 0.0%) i/s -    636.000  in  10.028939s
             render:    195.389  (± 0.5%) i/s -      1.957k in  10.016466s
     parse & render:     46.091  (± 0.0%) i/s -    464.000  in  10.067445s

After

Running benchmark for 10 seconds (with 5 seconds warmup).

Warming up --------------------------------------
              parse:     6.000  i/100ms
             render:    19.000  i/100ms
     parse & render:     4.000  i/100ms
Calculating -------------------------------------
              parse:     65.183  (± 0.0%) i/s -    654.000  in  10.033549s
             render:    195.648  (± 1.0%) i/s -      1.957k in  10.003511s
     parse & render:     46.917  (± 0.0%) i/s -    472.000  in  10.060782s