Add a symbolize transformer

[babacry]

Symbolizes single qubit gates by tags.

Example:
Input:

        0: ───X[phxz_0]───@───Y[phxz_1]───X───
                          │
        1: ───────────────@───────────────────

$ cirq.symbolize_single_qubit_gates_by_indexed_tags(c, tag_prefix="phxz")
Output:

        0: ───PhXZ(a=a0,x=x0,z=z0)───@───PhXZ(a=a1,x=x1,z=z1)───X───
                                     │
        1: ──────────────────────────@──────────────────────────────

where, a0,x0,z0,a1,x1,z1 are symbols.

Context: to be used in #6994.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.67%. Comparing base (b136ae8) to head (ede422f).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #7307   +/-   ##
=======================================
  Coverage   98.67%   98.67%           
=======================================
  Files        1111     1113    +2     
  Lines       96811    96856   +45     
=======================================
+ Hits        95528    95573   +45     
  Misses       1283     1283           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[babacry]

@NoureldinYosri , phxz symbolizer transformer! Could you help review?

[NoureldinYosri]

overall looks good but lets make the tag a class instead of a string, for example

@attrs.frozen
class SymbolizeTag:
    prefix: str

[babacry]

overall looks good but lets make the tag a class instead of a string, for example

@attrs.frozen
class SymbolizeTag:
    prefix: str

Good point, done.