fix: defaultFontFamily in webPreferences

[dsanders11]

Description of Change

This fix brought to you by clang-tidy, which detected the problem:

../../electron/shell/browser/web_contents_preferences.cc:430:71: warning: an integer is interpreted as a character code when assigning it to a string; if this is intended, cast the integer to the appropriate character type; if you want a string representation, use the appropriate conversion facility [bugprone-string-integer-assignment]
    prefs->standard_font_family_map[blink::web_pref::kCommonScript] = font;
                                                                      ^
../../electron/shell/browser/web_contents_preferences.cc:433:68: warning: an integer is interpreted as a character code when assigning it to a string; if this is intended, cast the integer to the appropriate character type; if you want a string representation, use the appropriate conversion facility [bugprone-string-integer-assignment]
    prefs->serif_font_family_map[blink::web_pref::kCommonScript] = font;
                                                                   ^
../../electron/shell/browser/web_contents_preferences.cc:436:73: warning: an integer is interpreted as a character code when assigning it to a string; if this is intended, cast the integer to the appropriate character type; if you want a string representation, use the appropriate conversion facility [bugprone-string-integer-assignment]
    prefs->sans_serif_font_family_map[blink::web_pref::kCommonScript] = font;
                                                                        ^
../../electron/shell/browser/web_contents_preferences.cc:439:68: warning: an integer is interpreted as a character code when assigning it to a string; if this is intended, cast the integer to the appropriate character type; if you want a string representation, use the appropriate conversion facility [bugprone-string-integer-assignment]
    prefs->fixed_font_family_map[blink::web_pref::kCommonScript] = font;
                                                                   ^
../../electron/shell/browser/web_contents_preferences.cc:442:70: warning: an integer is interpreted as a character code when assigning it to a string; if this is intended, cast the integer to the appropriate character type; if you want a string representation, use the appropriate conversion facility [bugprone-string-integer-assignment]
    prefs->cursive_font_family_map[blink::web_pref::kCommonScript] = font;
                                                                     ^
../../electron/shell/browser/web_contents_preferences.cc:445:70: warning: an integer is interpreted as a character code when assigning it to a string; if this is intended, cast the integer to the appropriate character type; if you want a string representation, use the appropriate conversion facility [bugprone-string-integer-assignment]
    prefs->fantasy_font_family_map[blink::web_pref::kCommonScript] = font;

Got broken by the refactors in #30193 (which shipped in v16) and there was no test coverage.

As far as I can tell, though, no one has reported the issue in that time, so that may speak to how used this option is.

Checklist

• PR description included and stakeholders cc'd
• npm test passes
• tests are changed or added
• PR release notes describe the change in a way relevant to app developers, and are capitalized, punctuated, and past tense.

Release Notes

Notes: Fixed an issue which made defaultFontFamily in webPreferences have no effect

[zcbenz]

Since this option is rarely used it might worth adding a if (!default_font_family_.empty()) test.

[release-clerk]

Release Notes Persisted

Fixed an issue which made defaultFontFamily in webPreferences have no effect

[trop]

I have automatically backported this PR to "25-x-y", please check out #37967

[trop]

I have automatically backported this PR to "24-x-y", please check out #37968

[trop]

I have automatically backported this PR to "23-x-y", please check out #37969

[trop]

I have automatically backported this PR to "22-x-y", please check out #37970