Made String.prototype.indexOf spec compliant.

[HalidOdat]

It changes the following:

• Made String.prototype.indexOf spec compliant.
• Added tests

[codecov]

Codecov Report

Merging #597 into master will increase coverage by 0.23%.
The diff coverage is 96.72%.

@@            Coverage Diff             @@
##           master     #597      +/-   ##
==========================================
+ Coverage   71.11%   71.34%   +0.23%     
==========================================
  Files         176      176              
  Lines       11503    11551      +48     
==========================================
+ Hits         8180     8241      +61     
+ Misses       3323     3310      -13     

Impacted Files	Coverage Δ
boa/src/builtins/string/mod.rs	46.19% <84.61%> (+3.53%)	⬆️
boa/src/builtins/string/tests.rs	100.00% <100.00%> (ø)

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[github-actions]

Benchmark for 80a5065

Click to view benchmark

Test	PR Benchmark	Master Benchmark	%
Arithmetic operations (Execution)	385.6±23.92ns	383.3±10.51ns	+0.60%
Arithmetic operations (Full)	162.1±3.99µs	174.6±8.02µs	-7.16%
Array access (Execution)	8.3±0.30µs	8.3±0.35µs	0.00%
Array access (Full)	177.3±3.63µs	188.7±10.61µs	-6.04%
Array creation (Execution)	3.4±0.06ms	3.4±0.08ms	0.00%
Array creation (Full)	3.6±0.10ms	3.8±0.13ms	-5.26%
Array pop (Execution)	1280.1±631.32µs	1221.6±48.90µs	+4.79%
Array pop (Full)	1501.2±141.03µs	1574.7±52.28µs	-4.67%
Boolean Object Access (Execution)	4.3±0.25µs	4.4±0.25µs	-2.27%
Boolean Object Access (Full)	174.0±6.36µs	179.9±8.68µs	-3.28%
Create Realm	152.7±4.98µs	152.3±3.72µs	+0.26%
Dynamic Object Property Access (Execution)	5.0±0.10µs	5.1±0.20µs	-1.96%
Dynamic Object Property Access (Full)	172.6±6.06µs	179.3±7.84µs	-3.74%
Expression (Lexer)	2.4±0.11µs	2.4±0.06µs	0.00%
Expression (Parser)	5.5±0.10µs	5.7±0.30µs	-3.51%
Fibonacci (Execution)	954.4±33.18µs	957.0±38.76µs	-0.27%
Fibonacci (Full)	1118.3±34.44µs	1157.7±30.77µs	-3.40%
For loop (Execution)	22.3±0.68µs	22.7±2.09µs	-1.76%
For loop (Full)	191.2±7.88µs	193.5±5.06µs	-1.19%
For loop (Lexer)	5.2±0.16µs	5.3±0.15µs	-1.89%
For loop (Parser)	14.0±0.44µs	14.4±0.84µs	-2.78%
Goal Symbols (Parser)	8.6±0.30µs	8.5±0.23µs	+1.18%
Hello World (Lexer)	823.1±29.66ns	823.0±18.45ns	+0.01%
Hello World (Parser)	2.2±0.09µs	2.2±0.25µs	0.00%
Long file (Parser)	6.3±0.10ms	6.5±0.23ms	-3.08%
Number Object Access (Execution)	3.3±0.08µs	3.3±0.12µs	0.00%
Number Object Access (Full)	170.9±5.03µs	173.7±5.93µs	-1.61%
Object Creation (Execution)	4.2±0.13µs	4.3±0.18µs	-2.33%
Object Creation (Full)	193.9±5.61µs	196.2±4.66µs	-1.17%
RegExp (Execution)	67.7±3.35µs	68.6±3.09µs	-1.31%
RegExp (Full)	256.5±11.74µs	258.0±10.14µs	-0.58%
RegExp Literal (Execution)	70.2±2.46µs	71.2±2.42µs	-1.40%
RegExp Literal (Full)	248.0±10.13µs	258.7±9.93µs	-4.14%
RegExp Literal Creation (Execution)	66.6±1.79µs	67.8±2.88µs	-1.77%
RegExp Literal Creation (Full)	289.8±7.90µs	304.4±15.70µs	-4.80%
Static Object Property Access (Execution)	4.4±0.09µs	4.4±0.05µs	0.00%
Static Object Property Access (Full)	171.4±5.34µs	175.0±5.66µs	-2.06%
String Object Access (Execution)	6.5±0.27µs	6.4±0.19µs	+1.56%
String Object Access (Full)	174.5±5.71µs	180.3±5.12µs	-3.22%
String comparison (Execution)	5.9±0.20µs	6.0±0.49µs	-1.67%
String comparison (Full)	174.6±6.08µs	178.1±7.69µs	-1.97%
String concatenation (Execution)	4.9±0.13µs	4.8±0.10µs	+2.08%
String concatenation (Full)	169.9±6.46µs	177.2±9.26µs	-4.12%
String copy (Execution)	3.6±0.10µs	3.6±0.17µs	0.00%
String copy (Full)	168.1±4.47µs	173.4±8.13µs	-3.06%
Symbols (Execution)	3.0±0.05µs	3.0±0.20µs	0.00%
Symbols (Full)	161.9±8.03µs	166.5±7.04µs	-2.76%